made necessary changes

Author: bishwaspraveen

sde_collections/serializers.py

@@ -239,12 +239,14 @@ def get_tdamm_tag(self, obj):
         return tags if tags is not None else []
 
     def get_document_type(self, obj):
-        if obj.document_type and obj.document_type != 0:
+        if obj.document_type and obj.document_type not in DocumentTypes.values:
+            raise ValueError(f"Invalid document type: {obj.document_type}")
+        elif obj.document_type is not None:
             return obj.get_document_type_display()
         elif obj.collection.document_type is not None:
             return obj.collection.get_document_type_display()
         else:
-            return "Unknown"
+            raise ValueError("No document type found")
 
     def get_title(self, obj):
         return obj.generated_title if obj.generated_title else obj.scraped_title