diff --git a/src/middlewared/middlewared/api/base/types/base/string.py b/src/middlewared/middlewared/api/base/types/base/string.py
index c0204d50ea2a4..827d263e6c984 100644
--- a/src/middlewared/middlewared/api/base/types/base/string.py
+++ b/src/middlewared/middlewared/api/base/types/base/string.py
@@ -51,7 +51,7 @@ def __get_pydantic_core_schema__(
 LongString = Annotated[
     LongStringWrapper,
     BeforeValidator(LongStringWrapper),
-    PlainSerializer(lambda x: undefined if x == undefined else x.value),
+    PlainSerializer(lambda x: x.value if isinstance(x, LongStringWrapper) else x),
 ]
 
 NonEmptyString = Annotated[str, Field(min_length=1)]
diff --git a/src/middlewared/middlewared/api/v25_04_0/cloud_backup.py b/src/middlewared/middlewared/api/v25_04_0/cloud_backup.py
index a5f80b22662f9..d67155c15db40 100644
--- a/src/middlewared/middlewared/api/v25_04_0/cloud_backup.py
+++ b/src/middlewared/middlewared/api/v25_04_0/cloud_backup.py
@@ -31,8 +31,8 @@ class CloudBackupCreate(BaseModel):
     pre_script: LongString = ""
     post_script: LongString = ""
     snapshot: bool = False
-    include: list[NonEmptyString]
-    exclude: list[NonEmptyString]
+    include: list[NonEmptyString] = []
+    exclude: list[NonEmptyString] = []
     args: LongString = ""
     enabled: bool = True
 
diff --git a/src/middlewared/middlewared/pytest/unit/api/base/types/test_base.py b/src/middlewared/middlewared/pytest/unit/api/base/types/test_base.py
index 966e80d3e1f85..7d917ac56e5a5 100644
--- a/src/middlewared/middlewared/pytest/unit/api/base/types/test_base.py
+++ b/src/middlewared/middlewared/pytest/unit/api/base/types/test_base.py
@@ -40,3 +40,11 @@ class SecretLongStringMethodArgs(BaseModel):
 
 def test_secret_long_string():
     assert accept_params(SecretLongStringMethodArgs, ["test"]) == ["test"]
+
+
+class LongStringDefaultMethodArgs(BaseModel):
+    str: LongString = ""
+
+
+def test_long_string_default():
+    assert accept_params(LongStringDefaultMethodArgs, []) == [""]
diff --git a/tests/api2/test_account_privilege_role_private_fields.py b/tests/api2/test_account_privilege_role_private_fields.py
index 91df0f1f3b477..40db7537c0475 100644
--- a/tests/api2/test_account_privilege_role_private_fields.py
+++ b/tests/api2/test_account_privilege_role_private_fields.py
@@ -168,7 +168,7 @@ def vmware():
     ("acme.dns.authenticator", dns_authenticator, {}, ["attributes"]),
     ("certificate", 1, {}, ["privatekey", "issuer"]),
     ("certificateauthority", certificateauthority, {}, ["privatekey", "issuer"]),
-    ("cloud_backup", cloudbackup, {}, ["credentials.provider", "password"]),
+    ("cloud_backup", cloudbackup, {}, ["credentials.provider.pass", "password"]),
     ("cloudsync.credentials", cloudsync_credential, {}, ["provider.pass"]),
     ("cloudsync", cloudsync, {}, ["credentials.provider", "encryption_password"]),
     ("disk", disk, {"extra": {"passwords": True}}, ["passwd"]),