diff --git a/cmem_plugin_uuid/transform/__init__.py b/cmem_plugin_uuid/transform/__init__.py
index ccb6200..c0e0cb4 100644
--- a/cmem_plugin_uuid/transform/__init__.py
+++ b/cmem_plugin_uuid/transform/__init__.py
@@ -55,8 +55,8 @@ class UUID1(TransformPlugin):
 
     def __init__(
         self,
-        node: str | None,
-        clock_seq: str | None,
+        node: str,
+        clock_seq: str,
     ):
         self.node = node_to_int(node) if node else None
         self.clock_seq = clock_seq_to_int(clock_seq) if clock_seq else None
@@ -107,7 +107,7 @@ class UUID3(TransformPlugin):
 
     def __init__(
         self,
-        namespace: str | None,
+        namespace: str,
         namespace_as_uuid: bool | None,
     ):
         self.namespace = namespace
@@ -128,7 +128,7 @@ def transform(self, inputs: Sequence[Sequence[str]]) -> Sequence[str]:
                     if self.namespace == "empty_value":
                         result += [str(uuid.UUID(hex=namespace_hex(_, 3), version=3))]
                     else:
-                        result += [str(uuid.uuid3(namespace_uuid, _))]
+                        result += [str(uuid.uuid3(namespace_uuid, _))]  # type: ignore[arg-type]
         else:
             raise OSError("No input for UUID3")
         return result
@@ -187,7 +187,7 @@ class UUID5(TransformPlugin):
 
     def __init__(
         self,
-        namespace: str | None,
+        namespace: str,
         namespace_as_uuid: bool | None,
     ):
         self.namespace = namespace
@@ -208,7 +208,7 @@ def transform(self, inputs: Sequence[Sequence[str]]) -> Sequence[str]:
                     if self.namespace == "empty_value":
                         result += [str(uuid.UUID(hex=namespace_hex(_, 5), version=5))]
                     else:
-                        result += [str(uuid.uuid5(namespace_uuid, _))]
+                        result += [str(uuid.uuid5(namespace_uuid, _))]  # type: ignore[arg-type]
         else:
             raise OSError("No input for UUID5")
         return result
@@ -235,7 +235,7 @@ def transform(self, inputs: Sequence[Sequence[str]]) -> Sequence[str]:
                 'Node value in the form "01:23:45:67:89:AB", 01-23-45-67-89-AB", or '
                 '"0123456789AB". If not given, a random 48-bit number is chosen.'
             ),
-            default_value=None,
+            default_value="",
         ),
         PluginParameter(
             name="clock_seq",
@@ -244,7 +244,7 @@ def transform(self, inputs: Sequence[Sequence[str]]) -> Sequence[str]:
                 "If clock sequence is given, it is used as the sequence number. "
                 "Otherwise a random 14-bit number is chosen."
             ),
-            default_value=None,
+            default_value="",
         ),
     ],
 )
@@ -253,8 +253,8 @@ class UUID6(TransformPlugin):
 
     def __init__(
         self,
-        node: str | None,
-        clock_seq: str | None,
+        node: str,
+        clock_seq: str,
     ):
         self.node = node_to_int(node) if node else None
         self.clock_seq = clock_seq_to_int(clock_seq) if clock_seq else None
diff --git a/cmem_plugin_uuid/utils.py b/cmem_plugin_uuid/utils.py
index 31d0b42..c648143 100644
--- a/cmem_plugin_uuid/utils.py
+++ b/cmem_plugin_uuid/utils.py
@@ -79,8 +79,8 @@ def namespace_hex(value: str, uuid_version: int) -> str | None:
 
 def get_namespace_uuid(
     namespace_as_uuid: bool | None,
-    namespace: str | None,
-    uuid_version: int | None,
+    namespace: str,
+    uuid_version: int,
 ) -> uuid.UUID | None:
     """Return namespace UUID"""
     namespace_uuid = None
diff --git a/tests/test_uuid.py b/tests/test_uuid.py
index 5b78487..aa06ee3 100644
--- a/tests/test_uuid.py
+++ b/tests/test_uuid.py
@@ -23,8 +23,8 @@
 def test_uuid1_without_input() -> None:
     """Test UUID1 without input"""
     result = UUID1(
-        node=None,
-        clock_seq=None,
+        node="",
+        clock_seq="",
     ).transform(inputs=[])
     assert len(result) == 1
     for item in result:
@@ -35,8 +35,8 @@ def test_uuid1_with_value_input() -> None:
     """Test UUID1 with value input"""
     input_values = [["input1"], ["input2"]]
     result = UUID1(
-        node=None,
-        clock_seq=None,
+        node="",
+        clock_seq="",
     ).transform(inputs=input_values)
     assert len(result) == 2  # noqa: PLR2004
     for item in result:
@@ -325,8 +325,8 @@ def test_uuid5_with_empty_namespace() -> None:
 def test_uuid6_without_input() -> None:
     """Test UUID6 without input"""
     result = UUID6(
-        node=None,
-        clock_seq=None,
+        node="",
+        clock_seq="",
     ).transform(inputs=[])
     assert len(result) == 1
     for item in result:
@@ -337,8 +337,8 @@ def test_uuid6_with_value_input() -> None:
     """Test UUID6 with value input"""
     input_values = [["input1"], ["input2"]]
     result = UUID6(
-        node=None,
-        clock_seq=None,
+        node="",
+        clock_seq="",
     ).transform(inputs=input_values)
     assert len(result) == 2  # noqa: PLR2004
     for item in result: