fix: modify remove_filtered_policy method to support filtering of empty strings (#12)

* Modify remove_filtered_policy method to support filtering of empty strings

* Update adapter.py

fix format

* fix adapter.py black format

Author: sanguinedab

casbin_pymongo_adapter/adapter.py

@@ -165,7 +165,9 @@ def remove_filtered_policy(self, sec, ptype, field_index, *field_values):
         if not (1 <= field_index + len(field_values) <= 6):
             return False
         query = {
-            f"v{index + field_index}": value for index, value in enumerate(field_values)
+            f"v{index + field_index}": value
+            for index, value in enumerate(field_values)
+            if value != ""
         }
         query["ptype"] = ptype
         results = self._collection.delete_many(query)