add comment for tombstone business revision issue

Signed-off-by: Hongjing Chen <[email protected]>

legal-api/src/legal_api/services/business_details_version.py

@@ -594,6 +594,8 @@ def resolution_json(resolution_revision) -> dict:
     @staticmethod
     def business_revision_json(business_revision, business_json):
         """Return the business revision as a json object."""
+        # business_revision for tombstone business will be None
+        # check and skip to return original business_json
         if not business_revision:
             return business_json
         business_json['hasRestrictions'] = business_revision.restriction_ind