diff --git a/setup.py b/setup.py
index a289552..c9a4113 100644
--- a/setup.py
+++ b/setup.py
@@ -11,7 +11,7 @@
 # This call to setup() does all the work
 setup(
     name="to_cei",
-    version="0.1.3",
+    version="0.1.4",
     description="to-CEI",
     long_description=long_description,
     long_description_content_type="text/markdown",
diff --git a/test/test_charter.py b/test/test_charter.py
index a440084..d073dfd 100644
--- a/test/test_charter.py
+++ b/test/test_charter.py
@@ -1,17 +1,17 @@
-from datetime import datetime
 import pathlib
+from datetime import datetime
 from typing import List
 
 import pytest
 from astropy.time.core import Time
 from lxml import etree
 
+from pytest_helpers import xp, xps
+from to_cei.charter import NO_DATE_TEXT, NO_DATE_VALUE, Charter
 from to_cei.config import CEI, CHARTER_NSS
 from to_cei.helpers import ln
-from to_cei.charter import NO_DATE_TEXT, NO_DATE_VALUE, Charter
 from to_cei.seal import Seal
 from to_cei.validator import Validator
-from pytest_helpers import xp, xps
 
 # --------------------------------------------------------------------#
 #                         Charter as a whole                         #
@@ -77,6 +77,7 @@ def test_is_valid_charter():
     )
     Validator().validate_cei(charter.to_xml())
 
+
 def test_writes_correct_file(tmp_path):
     d = tmp_path
     charter = Charter("1A")
@@ -86,6 +87,7 @@ def test_writes_correct_file(tmp_path):
     written = etree.parse(str(out))
     Validator().validate_cei(written.getroot())
 
+
 # --------------------------------------------------------------------#
 #                          Charter abstract                          #
 # --------------------------------------------------------------------#
@@ -117,6 +119,12 @@ def test_has_correct_xml_abstract():
     assert pers_name_xml.text == pers_name
 
 
+def test_has_no_abstract_for_empty_text():
+    abstract = ""
+    charter = Charter(id_text="1", abstract=abstract)
+    assert charter.abstract == None
+
+
 def test_raises_exception_for_incorrect_xml_abstract():
     incorrect_element = CEI.persName("A person")
     with pytest.raises(ValueError):
@@ -139,6 +147,12 @@ def test_has_correct_charter_archive():
     assert archive_xml.text == archive
 
 
+def test_has_no_archive_for_empty_text():
+    archive = ""
+    charter = Charter(id_text="1", archive=archive)
+    assert charter.archive == None
+
+
 # --------------------------------------------------------------------#
 #                       Charter bibliographies                       #
 # --------------------------------------------------------------------#
@@ -155,6 +169,18 @@ def test_has_correct_abstract_bibl():
     assert bibl.text == bibl_text
 
 
+def test_has_no_sources_for_empty_string():
+    bibl_texts = ""
+    sources = xp(
+        Charter(
+            id_text="1",
+            abstract_sources=bibl_texts,
+        ),
+        "/cei:text/cei:front/cei:sourceDesc/cei:sourceDescRegest/*",
+    )
+    assert len(sources) == 0
+
+
 def test_has_correct_abstract_sources():
     bibl_texts = ["Bibl a", "Bibl b"]
     sources = xp(
@@ -169,7 +195,7 @@ def test_has_correct_abstract_sources():
     assert sources[1].text == bibl_texts[1]
 
 
-def test_has_correct_transcription_bibl():
+def test_has_correct_transcription_source():
     bibl_text = "Bibl a"
     charter = Charter(
         id_text="1",
@@ -182,6 +208,15 @@ def test_has_correct_transcription_bibl():
     assert sources.text == bibl_text
 
 
+def test_has_no_transcription_sources_for_empty_text():
+    bibl_text = ""
+    charter = Charter(
+        id_text="1",
+        transcription_sources=bibl_text,
+    )
+    assert len(charter.transcription_sources) == 0
+
+
 def test_has_correct_transcription_sources():
     bibl_texts = ["Bibl a", "Bibl b"]
     sources = xp(
@@ -205,7 +240,7 @@ def test_has_correct_single_chancellary_remark():
     chancellary_remarks = "Remark"
     charter = Charter(id_text="1", chancellary_remarks=chancellary_remarks)
     assert isinstance(charter.chancellary_remarks, List)
-    assert charter._chancellary_remarks[0] == chancellary_remarks
+    assert charter.chancellary_remarks[0] == chancellary_remarks
     nota = xps(charter, "/cei:text/cei:body/cei:chDesc/cei:witnessOrig/cei:nota")
     assert nota.text == chancellary_remarks
 
@@ -213,13 +248,19 @@ def test_has_correct_single_chancellary_remark():
 def test_has_correct_chancellary_remarks_list():
     chancellary_remarks = ["Remark a", "Remark b"]
     charter = Charter(id_text="1", chancellary_remarks=chancellary_remarks)
-    assert charter._chancellary_remarks == chancellary_remarks
+    assert charter.chancellary_remarks == chancellary_remarks
     nota = xp(charter, "/cei:text/cei:body/cei:chDesc/cei:witnessOrig/cei:nota")
     assert len(nota) == 2
     assert nota[0].text == chancellary_remarks[0]
     assert nota[1].text == chancellary_remarks[1]
 
 
+def test_has_no_chancellary_remarks_for_empty_text():
+    chancellary_remarks = ""
+    charter = Charter(id_text="1", chancellary_remarks=chancellary_remarks)
+    assert len(charter.chancellary_remarks) == 0
+
+
 # --------------------------------------------------------------------#
 #                          Charter comments                          #
 # --------------------------------------------------------------------#
@@ -228,7 +269,7 @@ def test_has_correct_chancellary_remarks_list():
 def test_has_correct_comments():
     comments = ["Comment a", "Comment b"]
     charter = Charter(id_text="1", comments=comments)
-    assert charter._comments == comments
+    assert charter.comments == comments
     paragraphs = xp(
         charter,
         "/cei:text/cei:body/cei:chDesc/cei:diplomaticAnalysis/cei:p",
@@ -238,6 +279,12 @@ def test_has_correct_comments():
     assert paragraphs[1].text == comments[1]
 
 
+def test_has_no_comments_for_empty_string():
+    comments = ""
+    charter = Charter(id_text="1", comments=comments)
+    assert len(charter.comments) == 0
+
+
 # --------------------------------------------------------------------#
 #                         Charter condition                          #
 # --------------------------------------------------------------------#
@@ -254,6 +301,12 @@ def test_has_correct_charter_condition():
     assert condition_xml.text == condition
 
 
+def test_has_no_condition_for_empty_text():
+    condition = ""
+    charter = Charter(id_text="1", condition=condition)
+    assert charter.condition == None
+
+
 # --------------------------------------------------------------------#
 #                            Charter date                             #
 # --------------------------------------------------------------------#
@@ -268,6 +321,21 @@ def test_has_correct_date_range_with_99999999():
     assert date_xml.get("value") == NO_DATE_VALUE
 
 
+def test_has_no_date_for_empty_text():
+    charter = Charter(id_text="1", date="")
+    assert charter.date == None
+    assert charter.date_value == None
+
+
+def test_has_no_date_for_empty_value():
+    charter = Charter(id_text="1", date="unknown", date_value="")
+    assert charter.date == "unknown"
+    assert charter.date_value == None
+    date_xml = xps(charter, "/cei:text/cei:body/cei:chDesc/cei:issued/cei:date")
+    assert date_xml.text == "unknown"
+    assert date_xml.get("value") == NO_DATE_VALUE
+
+
 def test_has_correct_date_with_99999999():
     charter = Charter(id_text="1", date="unknown", date_value="99999999")
     assert charter.date == "unknown"
@@ -501,6 +569,12 @@ def test_has_correct_text_date_quote():
     assert date_quote_xml.text == date_quote
 
 
+def test_has_no_quote_for_empty_text():
+    date_quote = ""
+    charter = Charter(id_text="1", date_quote=date_quote)
+    assert charter.date_quote == None
+
+
 def test_has_correct_xml_date_quote():
     date_quote = CEI.quoteOriginaldatierung(
         "Original dating with ", CEI.sup("a"), " superscript"
@@ -536,6 +610,12 @@ def test_has_correct_charter_dimensions():
     assert dimensions_xml.text == dimensions
 
 
+def test_has_no_dimensions_for_empty_text():
+    dimensions = ""
+    charter = Charter(id_text="1", dimensions=dimensions)
+    assert charter.dimensions == None
+
+
 # --------------------------------------------------------------------#
 #                        Charter external url                        #
 # --------------------------------------------------------------------#
@@ -552,6 +632,12 @@ def test_has_correct_external_url():
     assert external_link_xml.get("target") == external_link
 
 
+def test_has_no_external_url_for_empty_text():
+    external_link = ""
+    charter = Charter(id_text="1", external_link=external_link)
+    assert charter.external_link == None
+
+
 def test_raises_exception_for_invalid_external_link():
     localhost = "http://localhost"
     with pytest.raises(ValueError):
@@ -563,7 +649,7 @@ def test_raises_exception_for_invalid_external_link():
 # --------------------------------------------------------------------#
 
 
-def test_has_correct_list_figures():
+def test_has_correct_list_graphic_urls():
     graphic_urls = ["Figure 1.jgp", "figure_2.png"]
     charter = Charter(id_text="1", graphic_urls=graphic_urls)
     assert charter.graphic_urls == graphic_urls
@@ -575,7 +661,7 @@ def test_has_correct_list_figures():
     assert graphics_xml[1].get("url") == graphic_urls[1]
 
 
-def test_has_correct_single_figures():
+def test_has_correct_single_graphic_url():
     graphic_urls = "Figure 1.jgp"
     charter = Charter(id_text="1", graphic_urls=graphic_urls)
     assert charter.graphic_urls[0] == graphic_urls
@@ -585,6 +671,12 @@ def test_has_correct_single_figures():
     assert graphics_xml.get("url") == graphic_urls
 
 
+def test_has_empty_graphic_urls_for_empty_text():
+    graphic_urls = ""
+    charter = Charter(id_text="1", graphic_urls=graphic_urls)
+    assert len(charter.graphic_urls) == 0
+
+
 # --------------------------------------------------------------------#
 #                         Charter footnotes                          #
 # --------------------------------------------------------------------#
@@ -603,6 +695,12 @@ def test_has_correct_footnotes():
     assert notes[1].text == footnotes[1]
 
 
+def test_has_no_footnotes_for_empty_text():
+    footnotes = ""
+    charter = Charter(id_text="1", footnotes=footnotes)
+    assert len(charter._footnotes) == 0
+
+
 # --------------------------------------------------------------------#
 #                             Charter id                             #
 # --------------------------------------------------------------------#
@@ -630,6 +728,12 @@ def test_has_correct_id_norm():
     assert idno.text == id_text
 
 
+def test_has_correct_id_norm_for_empty_text():
+    id = "1307-12-01"
+    charter = Charter(id_text=id, id_norm="")
+    assert charter.id_norm == id
+
+
 def test_has_correct_id_old():
     id_old = "123456 α"
     idno = xps(
@@ -638,6 +742,11 @@ def test_has_correct_id_old():
     assert idno.get("old") == id_old
 
 
+def test_has_no_id_old_for_empty_text():
+    charter = Charter(id_text="1307-12-01", id_old="")
+    assert charter.id_old == None
+
+
 def test_raises_exception_for_missing_id():
     with pytest.raises(ValueError):
         Charter(id_text="")
@@ -777,6 +886,12 @@ def test_has_correct_text_issued_place():
     assert issued_place_xml.text == issued_place
 
 
+def test_has_no_issued_place_for_empty_text():
+    issued_place = ""
+    charter = Charter(id_text="1", issued_place=issued_place)
+    assert charter.issued_place == None
+
+
 def test_has_correct_xml_issued_place():
     issued_place = CEI.placeName("Wien")
     charter = Charter(id_text="1", issued_place=issued_place)
@@ -810,6 +925,15 @@ def test_has_correct_abstract_with_text_issuer():
     assert issuer_xml.text == issuer
 
 
+def test_has_correct_abstract_with_empty_issuer():
+    abstract = (
+        "Konrad von Lintz, Caplan zu St. Pankraz, beurkundet den vorstehenden Vertrag."
+    )
+    issuer = ""
+    charter = Charter(id_text="1", abstract=abstract, issuer=issuer)
+    assert charter.issuer == None
+
+
 def test_has_correct_abstract_with_xml_issuer():
     abstract = (
         "Konrad von Lintz, Caplan zu St. Pankraz, beurkundet den vorstehenden Vertrag."
@@ -847,7 +971,13 @@ def test_has_correct_language():
         charter,
         "/cei:text/cei:body/cei:chDesc/cei:lang_MOM",
     )
-    language_xml.text == language
+    assert language_xml.text == language
+
+
+def test_has_no_language_for_empty_string():
+    language = ""
+    charter = Charter(id_text="1", language=language)
+    assert charter.language == None
 
 
 # --------------------------------------------------------------------#
@@ -868,6 +998,12 @@ def test_has_correct_literature():
     assert literature_xml[1].text == literature[1]
 
 
+def test_has_no_literature_for_empty_text():
+    literature = ""
+    charter = Charter(id_text="1", literature=literature)
+    assert len(charter.literature) == 0
+
+
 def test_has_correct_literature_abstracts():
     literature_abstracts = ["Entry 1", "Entry 2"]
     charter = Charter(id_text="1", literature_abstracts=literature_abstracts)
@@ -881,6 +1017,12 @@ def test_has_correct_literature_abstracts():
     assert literature_abstracts_xml[1].text == literature_abstracts[1]
 
 
+def test_has_no_literature_abstracts_for_empty_text():
+    literature_abstracts = ""
+    charter = Charter(id_text="1", literature_abstracts=literature_abstracts)
+    assert len(charter.literature_abstracts) == 0
+
+
 def test_has_correct_literature_depictions():
     literature_depictions = ["Entry 1", "Entry 2"]
     charter = Charter(id_text="1", literature_depictions=literature_depictions)
@@ -894,6 +1036,12 @@ def test_has_correct_literature_depictions():
     assert literature_depictions_xml[1].text == literature_depictions[1]
 
 
+def test_has_no_literature_depictions_for_empty_text():
+    literature_depictions = ""
+    charter = Charter(id_text="1", literature_depictions=literature_depictions)
+    assert len(charter.literature_depictions) == 0
+
+
 def test_has_correct_literature_editions():
     literature_editions = ["Entry 1", "Entry 2"]
     charter = Charter(id_text="1", literature_editions=literature_editions)
@@ -907,6 +1055,12 @@ def test_has_correct_literature_editions():
     assert literature_editions_xml[1].text == literature_editions[1]
 
 
+def test_has_no_literature_editions_for_empty_text():
+    literature_editions = ""
+    charter = Charter(id_text="1", literature_editions=literature_editions)
+    assert len(charter.literature_editions) == 0
+
+
 def test_has_correct_literature_secondary():
     literature_secondary = ["Entry 1", "Entry 2"]
     charter = Charter(id_text="1", literature_secondary=literature_secondary)
@@ -920,6 +1074,12 @@ def test_has_correct_literature_secondary():
     assert literature_secondary_xml[1].text == literature_secondary[1]
 
 
+def test_has_no_literature_secondary_for_empty_text():
+    literature_secondary = ""
+    charter = Charter(id_text="1", literature_secondary=literature_secondary)
+    assert len(charter.literature_secondary) == 0
+
+
 # --------------------------------------------------------------------#
 #                          Charter material                          #
 # --------------------------------------------------------------------#
@@ -936,6 +1096,12 @@ def test_has_correct_material():
     assert material_xml.text == material
 
 
+def test_has_no_material_for_empty_text():
+    material = ""
+    charter = Charter(id_text="1", material=material)
+    assert charter.material == None
+
+
 # --------------------------------------------------------------------#
 #                        Charter notarial authentication             #
 # --------------------------------------------------------------------#
@@ -952,6 +1118,12 @@ def test_has_correct_text_notarial_authentication():
     assert notarial_authentication_xml.text == notarial_authentication
 
 
+def test_has_no_text_notarial_authentication_for_empty_text():
+    notarial_authentication = ""
+    charter = Charter(id_text="1", notarial_authentication=notarial_authentication)
+    assert charter.notarial_authentication == None
+
+
 def test_has_correct_xml_notarial_authentication():
     notarial_authentication = CEI.notariusDesc("An xml notarial authentication")
     charter = Charter(id_text="1", notarial_authentication=notarial_authentication)
@@ -988,6 +1160,15 @@ def test_has_correct_abstract_with_text_recipient():
     assert recipient_xml.text == recipient
 
 
+def test_has_abstract_without_text_recipient_for_empty_text():
+    abstract = (
+        "Konrad von Lintz, Caplan zu St. Pankraz, beurkundet den vorstehenden Vertrag."
+    )
+    recipient = ""
+    charter = Charter(id_text="1", abstract=abstract, recipient=recipient)
+    assert charter.recipient == None
+
+
 def test_has_correct_abstract_with_xml_recipient():
     abstract = (
         "Konrad von Lintz, Caplan zu St. Pankraz, beurkundet den vorstehenden Vertrag."
@@ -1034,6 +1215,11 @@ def test_has_correct_seal_description_xml():
     assert seals_xml[1].text == "Seal 2"
 
 
+def test_has_no_seal_description_for_empty_text():
+    charter = Charter(id_text="1", seals="")
+    assert charter.seals == None
+
+
 def test_has_correct_seal_text_description():
     seals = "2 Siegel"
     charter = Charter(id_text="1", seals=seals)
@@ -1111,6 +1297,12 @@ def test_has_correct_text_transcription():
     assert transcription_xml.text == transcription
 
 
+def test_has_no_text_transcription_for_empty_text():
+    transcription = ""
+    charter = Charter(id_text="1", transcription=transcription)
+    assert charter.transcription == None
+
+
 def test_has_correct_xml_transcription():
     transcription = CEI.tenor("Tenor with ", CEI.sup("a"), " superscript")
     charter = Charter(id_text="1", transcription=transcription)
@@ -1143,6 +1335,12 @@ def test_has_correct_tradition():
     assert tradition_xml.text == tradition
 
 
+def test_has_no_tradition_for_empty_text():
+    tradition = ""
+    charter = Charter(id_text="1", tradition=tradition)
+    assert charter.tradition == None
+
+
 # --------------------------------------------------------------------#
 #                            Charter type                            #
 # --------------------------------------------------------------------#
diff --git a/to_cei/charter.py b/to_cei/charter.py
index 4091c50..e4049ae 100644
--- a/to_cei/charter.py
+++ b/to_cei/charter.py
@@ -149,42 +149,42 @@ class Charter(XmlAssembler):
     def __init__(
         self,
         id_text: str,
-        abstract: str | etree._Element = None,
-        abstract_sources: str | List[str] = [],
-        archive: str = None,
-        chancellary_remarks: str | List[str] = [],
-        comments: str | List[str] = [],
-        condition: str = None,
-        date: str | etree._Element = None,
-        date_quote: str | etree._Element = None,
-        date_value: DateValue = None,
-        dimensions: str = None,
-        external_link: str = None,
-        footnotes: str | List[str] = [],
-        graphic_urls: str | List[str] = [],
-        id_norm: str = None,
-        id_old: str = None,
-        index: List[str | etree._Element] = [],
-        index_geo_features: List[str | etree._Element] = [],
-        index_organizations: List[str | etree._Element] = [],
-        index_persons: List[str | etree._Element] = [],
-        index_places: List[str | etree._Element] = [],
-        issued_place: str | etree._Element = None,
-        issuer: str | etree._Element = None,
-        language: str = None,
-        literature: str | List[str] = [],
-        literature_abstracts: str | List[str] = [],
-        literature_depictions: str | List[str] = [],
-        literature_editions: str | List[str] = [],
-        literature_secondary: str | List[str] = [],
-        material: str = None,
-        notarial_authentication: str | etree._Element = None,
-        recipient: str | etree._Element = None,
-        seals: etree._Element | str | Seal | List[str] | List[Seal] = None,
-        tradition: str = None,
-        transcription: str | etree._Element = None,
-        transcription_sources: str | List[str] = [],
-        witnesses: List[str | etree._Element] = [],
+        abstract: Optional[str | etree._Element] = None,
+        abstract_sources: Optional[str | List[str]] = [],
+        archive: Optional[str] = None,
+        chancellary_remarks: Optional[str | List[str]] = [],
+        comments: Optional[str | List[str]] = [],
+        condition: Optional[str] = None,
+        date: Optional[str | etree._Element] = None,
+        date_quote: Optional[str | etree._Element] = None,
+        date_value: Optional[DateValue] = None,
+        dimensions: Optional[str] = None,
+        external_link: Optional[str] = None,
+        footnotes: Optional[str | List[str]] = [],
+        graphic_urls: Optional[str | List[str]] = [],
+        id_norm: Optional[str] = None,
+        id_old: Optional[str] = None,
+        index: Optional[List[str | etree._Element]] = [],
+        index_geo_features: Optional[List[str | etree._Element]] = [],
+        index_organizations: Optional[List[str | etree._Element]] = [],
+        index_persons: Optional[List[str | etree._Element]] = [],
+        index_places: Optional[List[str | etree._Element]] = [],
+        issued_place: Optional[str | etree._Element] = None,
+        issuer: Optional[str | etree._Element] = None,
+        language: Optional[str] = None,
+        literature: Optional[str | List[str]] = [],
+        literature_abstracts: Optional[str | List[str]] = [],
+        literature_depictions: Optional[str | List[str]] = [],
+        literature_editions: Optional[str | List[str]] = [],
+        literature_secondary: Optional[str | List[str]] = [],
+        material: Optional[str] = None,
+        notarial_authentication: Optional[str | etree._Element] = None,
+        recipient: Optional[str | etree._Element] = None,
+        seals: Optional[etree._Element | str | Seal | List[str] | List[Seal]] = None,
+        tradition: Optional[str] = None,
+        transcription: Optional[str | etree._Element] = None,
+        transcription_sources: Optional[str] | List[str] = [],
+        witnesses: Optional[List[str | etree._Element]] = [],
     ) -> None:
         """
         Creates a new charter object.
@@ -281,7 +281,7 @@ def abstract(self):
         return self._abstract
 
     @abstract.setter
-    def abstract(self, value: str | etree._Element = None):
+    def abstract(self, value: Optional[str | etree._Element] = None):
         if self.issuer is not None and isinstance(self.issuer, etree._Element):
             raise ValueError(
                 "XML element content for both issuer and abstract is not allowed, please join the issuer in the XML abstract yourself"
@@ -293,47 +293,59 @@ def abstract_sources(self):
         return self._abstract_sources
 
     @abstract_sources.setter
-    def abstract_sources(self, value: str | List[str] = []):
-        self._abstract_sources = value if isinstance(value, List) else [value]
+    def abstract_sources(self, value: Optional[str | List[str]] = []):
+        self._abstract_sources = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else (value if isinstance(value, List) else [value])
+        )
 
     @property
     def archive(self):
         return self._archive
 
     @archive.setter
-    def archive(self, value: str = None):
-        self._archive = value
+    def archive(self, value: Optional[str] = None):
+        self._archive = value if value is not None and len(value) else None
 
     @property
     def chancellary_remarks(self):
         return self._chancellary_remarks
 
     @chancellary_remarks.setter
-    def chancellary_remarks(self, value: str | List[str] = []):
-        self._chancellary_remarks = [value] if isinstance(value, str) else value
+    def chancellary_remarks(self, value: Optional[str | List[str]] = []):
+        self._chancellary_remarks = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def comments(self):
         return self._comments
 
     @comments.setter
-    def comments(self, value: str | List[str] = []):
-        self._comments = [value] if isinstance(value, str) else value
+    def comments(self, value: Optional[str | List[str]] = []):
+        self._comments = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def condition(self):
         return self._condition
 
     @condition.setter
-    def condition(self, value: str = None):
-        self._condition = value
+    def condition(self, value: Optional[str] = None):
+        self._condition = value if isinstance(value, str) and len(value) else None
 
     @property
     def date(self):
         return self._date
 
     @date.setter
-    def date(self, value: str | etree._Element = None):
+    def date(self, value: Optional[str | etree._Element] = None):
         self._date = validate_element(value, "date", "dateRange")
 
     @property
@@ -341,7 +353,7 @@ def date_quote(self):
         return self._date_quote
 
     @date_quote.setter
-    def date_quote(self, value: str | etree._Element = None):
+    def date_quote(self, value: Optional[str | etree._Element] = None):
         self._date_quote = validate_element(value, "quoteOriginaldatierung")
 
     @property
@@ -349,14 +361,16 @@ def date_value(self):
         return self._date_value
 
     @date_value.setter
-    def date_value(self, value: DateValue = None):
+    def date_value(self, value: Optional[DateValue] = None):
         # Don't allow to directly set date values if an XML date element is present
         if isinstance(self.date, etree._Element):
             raise ValueError(
                 "Not allowed to set date value directly if the date is already an XML element."
             )
         # Unknown MOM date (99999999)
-        elif (isinstance(value, str) and value == NO_DATE_VALUE) or (
+        elif (
+            isinstance(value, str) and (value == NO_DATE_VALUE or not len(value))
+        ) or (
             isinstance(value, Tuple)
             and len(value) == 2
             and value[0] == NO_DATE_VALUE
@@ -408,16 +422,18 @@ def dimensions(self):
         return self._dimensions
 
     @dimensions.setter
-    def dimensions(self, value: str = None):
-        self._dimensions = value
+    def dimensions(self, value: Optional[str] = None):
+        self._dimensions = value if isinstance(value, str) and len(value) else None
 
     @property
     def external_link(self):
         return self._external_link
 
     @external_link.setter
-    def external_link(self, value: str = None):
-        if value and not re.match(SIMPLE_URL_REGEX, value):
+    def external_link(self, value: Optional[str] = None):
+        if not isinstance(value, str) or len(value) == 0:
+            return None
+        if not re.match(SIMPLE_URL_REGEX, value):
             raise ValueError(
                 "'{}' does not look like a valid external URL. If you think it is valid, please contact the to-CEI library maintainers and tell them.".format(
                     value
@@ -430,32 +446,40 @@ def footnotes(self):
         return self._footnotes
 
     @footnotes.setter
-    def footnotes(self, value):
-        self._footnotes = value
+    def footnotes(self, value: Optional[str | List[str]] = []):
+        self._footnotes = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def graphic_urls(self):
         return self._graphic_urls
 
     @graphic_urls.setter
-    def graphic_urls(self, value: str | List[str] = []):
-        self._graphic_urls = value if isinstance(value, List) else [value]
+    def graphic_urls(self, value: Optional[str | List[str]] = []):
+        self._graphic_urls = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def id_norm(self):
         return quote(self._id_norm if self._id_norm else self.id_text)
 
     @id_norm.setter
-    def id_norm(self, value: str = None):
-        self._id_norm = value
+    def id_norm(self, value: Optional[str] = None):
+        self._id_norm = value if isinstance(value, str) and len(value) else None
 
     @property
     def id_old(self):
         return self._id_old
 
     @id_old.setter
-    def id_old(self, value: str = None):
-        self._id_old = value
+    def id_old(self, value: Optional[str] = None):
+        self._id_old = value if isinstance(value, str) and len(value) else None
 
     @property
     def id_text(self):
@@ -470,47 +494,47 @@ def index(self):
         return self._index
 
     @index.setter
-    def index(self, value: List[str | etree._Element] = []):
-        self._index = [validate_element(item, "index") for item in value]  # type: ignore
+    def index(self, value: Optional[List[str | etree._Element]] = []):
+        self._index = [validate_element(item, "index") for item in value] if isinstance(value, List) else []  # type: ignore
 
     @property
     def index_geo_features(self):
         return self._index_geo_features
 
     @index_geo_features.setter
-    def index_geo_features(self, value: List[str | etree._Element] = []):
-        self._index_geo_features = [validate_element(item, "geogName") for item in value]  # type: ignore
+    def index_geo_features(self, value: Optional[List[str | etree._Element]] = []):
+        self._index_geo_features = [validate_element(item, "geogName") for item in value] if isinstance(value, List) else []  # type: ignore
 
     @property
     def index_organizations(self):
         return self._index_organizations
 
     @index_organizations.setter
-    def index_organizations(self, value: List[str | etree._Element] = []):
-        self._index_organizations = [validate_element(item, "orgName") for item in value]  # type: ignore
+    def index_organizations(self, value: Optional[List[str | etree._Element]] = []):
+        self._index_organizations = [validate_element(item, "orgName") for item in value] if isinstance(value, List) else []  # type: ignore
 
     @property
     def index_persons(self):
         return self._index_persons
 
     @index_persons.setter
-    def index_persons(self, value: List[str | etree._Element] = []):
-        self._index_persons = [validate_element(item, "persName") for item in value]  # type: ignore
+    def index_persons(self, value: Optional[List[str | etree._Element]] = []):
+        self._index_persons = [validate_element(item, "persName") for item in value] if isinstance(value, List) else []  # type: ignore
 
     @property
     def index_places(self):
         return self._index_places
 
     @index_places.setter
-    def index_places(self, value: List[str | etree._Element] = []):
-        self._index_places = [validate_element(item, "placeName") for item in value]  # type: ignore
+    def index_places(self, value: Optional[List[str | etree._Element]] = []):
+        self._index_places = [validate_element(item, "placeName") for item in value] if isinstance(value, List) else []  # type: ignore
 
     @property
     def issued_place(self):
         return self._issued_place
 
     @issued_place.setter
-    def issued_place(self, value: str | etree._Element = None):
+    def issued_place(self, value: Optional[str | etree._Element] = None):
         self._issued_place = validate_element(value, "placeName")
 
     @property
@@ -518,7 +542,7 @@ def issuer(self):
         return self._issuer
 
     @issuer.setter
-    def issuer(self, value: str | etree._Element = None):
+    def issuer(self, value: Optional[str | etree._Element] = None):
         if value is not None and isinstance(self.abstract, etree._Element):
             raise ValueError(
                 "XML element content for both issuer and abstract is not allowed, please join the issuer in the XML abstract yourself"
@@ -530,63 +554,83 @@ def language(self):
         return self._language
 
     @language.setter
-    def language(self, value: str = None):
-        self._language = value
+    def language(self, value: Optional[str] = None):
+        self._language = value if isinstance(value, str) and len(value) else None
 
     @property
     def literature(self):
         return self._literature
 
     @literature.setter
-    def literature(self, value: str | List[str] = []):
-        self._literature = value if isinstance(value, List) else [value]
+    def literature(self, value: Optional[str | List[str]] = []):
+        self._literature = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def literature_abstracts(self):
         return self._literature_abstracts
 
     @literature_abstracts.setter
-    def literature_abstracts(self, value: str | List[str] = []):
-        self._literature_abstracts = value if isinstance(value, List) else [value]
+    def literature_abstracts(self, value: Optional[str | List[str]] = []):
+        self._literature_abstracts = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def literature_depictions(self):
         return self._literature_depictions
 
     @literature_depictions.setter
-    def literature_depictions(self, value: str | List[str] = []):
-        self._literature_depictions = value if isinstance(value, List) else [value]
+    def literature_depictions(self, value: Optional[str | List[str]] = []):
+        self._literature_depictions = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def literature_editions(self):
         return self._literature_editions
 
     @literature_editions.setter
-    def literature_editions(self, value: str | List[str] = []):
-        self._literature_editions = value if isinstance(value, List) else [value]
+    def literature_editions(self, value: Optional[str | List[str]] = []):
+        self._literature_editions = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def literature_secondary(self):
         return self._literature_secondary
 
     @literature_secondary.setter
-    def literature_secondary(self, value: str | List[str] = []):
-        self._literature_secondary = value if isinstance(value, List) else [value]
+    def literature_secondary(self, value: Optional[str | List[str]] = []):
+        self._literature_secondary = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def material(self):
         return self._material
 
     @material.setter
-    def material(self, value: str = None):
-        self._material = value
+    def material(self, value: Optional[str] = None):
+        self._material = value if isinstance(value, str) and len(value) else None
 
     @property
     def notarial_authentication(self):
         return self._notarial_authentication
 
     @notarial_authentication.setter
-    def notarial_authentication(self, value: str | etree._Element = None):
+    def notarial_authentication(self, value: Optional[str | etree._Element] = None):
         self._notarial_authentication = validate_element(value, "notariusDesc")
 
     @property
@@ -594,7 +638,7 @@ def recipient(self):
         return self._recipient
 
     @recipient.setter
-    def recipient(self, value: str | etree._Element = None):
+    def recipient(self, value: Optional[str | etree._Element] = None):
         if value is not None and isinstance(self.abstract, etree._Element):
             raise ValueError(
                 "XML element content for both recipient and abstract is not allowed, please join the recipient in the XML abstract yourself"
@@ -608,8 +652,10 @@ def seals(self):
     @seals.setter
     def seals(
         self,
-        value: etree._Element | str | Seal | List[str] | List[Seal] = None,
+        value: Optional[etree._Element | str | Seal | List[str] | List[Seal]] = None,
     ):
+        if value is None or isinstance(value, str) and len(value) == 0:
+            return None
         validated = (
             validate_element(value, "sealDesc")
             if isinstance(value, etree._Element)
@@ -625,15 +671,15 @@ def tradition(self):
         return self._tradition
 
     @tradition.setter
-    def tradition(self, value: str = None):
-        self._tradition = value
+    def tradition(self, value: Optional[str] = None):
+        self._tradition = value if isinstance(value, str) and len(value) else None
 
     @property
     def transcription(self):
         return self._transcription
 
     @transcription.setter
-    def transcription(self, value: str | etree._Element = None):
+    def transcription(self, value: Optional[str | etree._Element] = None):
         self._transcription = validate_element(value, "tenor")
 
     @property
@@ -641,16 +687,20 @@ def transcription_sources(self):
         return self._transcription_sources
 
     @transcription_sources.setter
-    def transcription_sources(self, value: str | List[str] = []):
-        self._transcription_sources = value if isinstance(value, List) else [value]
+    def transcription_sources(self, value: Optional[str | List[str]] = []):
+        self._transcription_sources = (
+            []
+            if value is None or (isinstance(value, str) and not len(value))
+            else ([value] if isinstance(value, str) else value)
+        )
 
     @property
     def witnesses(self):
         return self._witnesses
 
     @witnesses.setter
-    def witnesses(self, value: List[str | etree._Element] = []):
-        self._witnesses = [validate_element(item, "persName") for item in value]  # type: ignore
+    def witnesses(self, value: Optional[List[str | etree._Element]] = []):
+        self._witnesses = [validate_element(item, "persName") for item in value] if isinstance(value, List) else []  # type: ignore
 
     # --------------------------------------------------------------------#
     #                        Private CEI creators                        #
@@ -989,10 +1039,10 @@ def _create_cei_witness_orig(self) -> Optional[etree._Element]:
     def to_xml(self) -> etree._Element:
         return self._create_cei_text()
 
-    def to_file(self, folder: str = None):
+    def to_file(self, folder: Optional[str] = None):
         """Writes the xml representation of the charter to a file. The filename is generated from the normalized charter id.
 
         Args:
-            folder (str): The folder to write the file to. If this is ommitted, the file is written to the place where the script is 
+            folder (str): The folder to write the file to. If this is ommitted, the file is written to the place where the script is
         """
         return super(Charter, self).to_file(self.id_norm + ".cei", folder=folder)
diff --git a/to_cei/charter_group.py b/to_cei/charter_group.py
index 264f644..b5fcf8c 100644
--- a/to_cei/charter_group.py
+++ b/to_cei/charter_group.py
@@ -1,4 +1,4 @@
-from typing import List
+from typing import List, Optional
 
 from lxml import etree
 
@@ -46,7 +46,7 @@ def to_xml(self) -> etree._Element:
         )
         return xml
 
-    def to_file(self, folder: str = None):
+    def to_file(self, folder: Optional[str] = None):
         return super(CharterGroup, self).to_file(
             self.name.lower().replace(" ", "_") + ".cei.group", folder=folder
         )
diff --git a/to_cei/helpers.py b/to_cei/helpers.py
index c0cb892..b357b9b 100644
--- a/to_cei/helpers.py
+++ b/to_cei/helpers.py
@@ -31,6 +31,8 @@ def ns(element: etree._Element) -> str:
 def validate_element(
     value: Optional[str | etree._Element], *tags: str
 ) -> Optional[str | etree._Element]:
+    if isinstance(value, str) and not len(value):
+        return None
     if isinstance(value, etree._Element):
         if ns(value) != CEI_NS:
             raise ValueError(
diff --git a/to_cei/seal.py b/to_cei/seal.py
index 9d9e30c..c4ac047 100644
--- a/to_cei/seal.py
+++ b/to_cei/seal.py
@@ -16,11 +16,11 @@ class Seal(XmlAssembler):
 
     def __init__(
         self,
-        condition: str = None,
-        dimensions: str = None,
-        legend: str | List[Tuple[str, str]] = [],
-        material: str = None,
-        sigillant: str | etree._Element = None,
+        condition: Optional[str] = None,
+        dimensions: Optional[str] = None,
+        legend: Optional[str | List[Tuple[str, str]]] = [],
+        material: Optional[str] = None,
+        sigillant: Optional[str | etree._Element] = None,
     ) -> None:
         """
         Creates a seal instance.
@@ -52,39 +52,43 @@ def condition(self):
         return self._condition
 
     @condition.setter
-    def condition(self, value: str = None):
-        self._condition = value
+    def condition(self, value: Optional[str] = None):
+        self._condition = value if isinstance(value, str) and len(value) else None
 
     @property
     def dimensions(self):
         return self._dimensions
 
     @dimensions.setter
-    def dimensions(self, value: str = None):
-        self._dimensions = value
+    def dimensions(self, value: Optional[str] = None):
+        self._dimensions = value if isinstance(value, str) and len(value) else None
 
     @property
     def legend(self):
         return self._legend
 
     @legend.setter
-    def legend(self, value: str | List[Tuple[str, str]] = []):
-        self._legend = value
+    def legend(self, value: Optional[str | List[Tuple[str, str]]] = []):
+        self._legend = (
+            []
+            if value is None or (isinstance(value, str) and len(value) == 0)
+            else value
+        )
 
     @property
     def material(self):
         return self._material
 
     @material.setter
-    def material(self, value: str = None):
-        self._material = value
+    def material(self, value: Optional[str] = None):
+        self._material = value if isinstance(value, str) and len(value) else None
 
     @property
     def sigillant(self):
         return self._sigillant
 
     @sigillant.setter
-    def sigillant(self, value: str | etree._Element = None):
+    def sigillant(self, value: Optional[str | etree._Element] = None):
         self._sigillant = validate_element(value, "persName", "orgName")
 
     # --------------------------------------------------------------------#
diff --git a/to_cei/xml_assembler.py b/to_cei/xml_assembler.py
index c1c9b05..d489d40 100644
--- a/to_cei/xml_assembler.py
+++ b/to_cei/xml_assembler.py
@@ -24,7 +24,7 @@ def to_string(self) -> str:
     def to_file(
         self,
         name: str,
-        folder: str | Path = None,
+        folder: Optional[str | Path] = None,
         inclusive_ns_prefixes: List[str] = [],
     ):
         xml = self.to_xml()