FIX: added check for None values in identified cache

src/caoscrawler/identified_cache.py

@@ -53,7 +53,9 @@ def _value_representation(value):
     #       to allow the special case of Files as values of properties.
     #       We need to review the completeness of all the cases here, as the cache
     #       is crucial for correct identification of insertion and updates.
-    if isinstance(value, db.File):
+    if value is None:
+        return "None"
+    elif isinstance(value, db.File):
         return str(value.path)
     elif isinstance(value, db.Entity):
         if value.id is not None:
@@ -66,6 +68,7 @@ def _value_representation(value):
           or isinstance(value, datetime)):
         return str(value)
     else:
+        breakpoint()
         raise ValueError(f"Unknown datatype of the value: {value}")