diff --git a/sdk/basyx/aas/adapter/json/json_serialization.py b/sdk/basyx/aas/adapter/json/json_serialization.py
index 0b0df016..8b582068 100644
--- a/sdk/basyx/aas/adapter/json/json_serialization.py
+++ b/sdk/basyx/aas/adapter/json/json_serialization.py
@@ -476,7 +476,8 @@ def _blob_to_json(cls, obj: model.Blob) -> Dict[str, object]:
         :return: dict with the serialized attributes of this object
         """
         data = cls._abstract_classes_to_json(obj)
-        data['contentType'] = obj.content_type
+        if obj.content_type is not None:
+            data['contentType'] = obj.content_type
         if obj.value is not None:
             data['value'] = base64.b64encode(obj.value).decode()
         return data
@@ -490,7 +491,8 @@ def _file_to_json(cls, obj: model.File) -> Dict[str, object]:
         :return: dict with the serialized attributes of this object
         """
         data = cls._abstract_classes_to_json(obj)
-        data['contentType'] = obj.content_type
+        if obj.content_type is not None:
+            data['contentType'] = obj.content_type
         if obj.value is not None:
             data['value'] = obj.value
         return data
diff --git a/sdk/basyx/aas/model/submodel.py b/sdk/basyx/aas/model/submodel.py
index 9e7321c4..fb1ccc5a 100644
--- a/sdk/basyx/aas/model/submodel.py
+++ b/sdk/basyx/aas/model/submodel.py
@@ -464,7 +464,7 @@ class Blob(DataElement):
 
     def __init__(self,
                  id_short: Optional[base.NameType],
-                 content_type: base.ContentType,
+                 content_type: Optional[base.ContentType] = None,
                  value: Optional[base.BlobType] = None,
                  display_name: Optional[base.MultiLanguageNameType] = None,
                  category: Optional[base.NameType] = None,
@@ -482,7 +482,7 @@ def __init__(self,
         super().__init__(id_short, display_name, category, description, parent, semantic_id, qualifier, extension,
                          supplemental_semantic_id, embedded_data_specifications)
         self.value: Optional[base.BlobType] = value
-        self.content_type: base.ContentType = content_type
+        self.content_type: Optional[base.ContentType] = content_type
 
 
 @_string_constraints.constrain_content_type("content_type")
@@ -518,7 +518,7 @@ class File(DataElement):
 
     def __init__(self,
                  id_short: Optional[base.NameType],
-                 content_type: base.ContentType,
+                 content_type: Optional[base.ContentType] = None,
                  value: Optional[base.PathType] = None,
                  display_name: Optional[base.MultiLanguageNameType] = None,
                  category: Optional[base.NameType] = None,
@@ -536,7 +536,7 @@ def __init__(self,
         super().__init__(id_short, display_name, category, description, parent, semantic_id, qualifier, extension,
                          supplemental_semantic_id, embedded_data_specifications)
         self.value: Optional[base.PathType] = value
-        self.content_type: base.ContentType = content_type
+        self.content_type: Optional[base.ContentType] = content_type
 
 
 class ReferenceElement(DataElement):