diff --git a/src/caoscrawler/identified_cache.py b/src/caoscrawler/identified_cache.py
index 7b680b5ab69b74469c0ce064c91e56bbef7340ed..b5ee1baa66cbbc960c5551c9a1fac71061c820d9 100644
--- a/src/caoscrawler/identified_cache.py
+++ b/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}")