Fix error can't bulk-insert empty slice []*pgadapter.CasbinRule

adapter.go

@@ -211,10 +211,13 @@ func (a *Adapter) SavePolicy(model model.Model) error {
 		}
 	}
 
-	_, err = a.db.Model(&lines).
-		OnConflict("DO NOTHING").
-		Insert()
-	return err
+	if len(lines) > 0 {
+		_, err = a.db.Model(&lines).
+			OnConflict("DO NOTHING").
+			Insert()
+		return err
+	}
+	return nil
 }
 
 // AddPolicy adds a policy rule to the storage.

adapter_test.go

@@ -221,6 +221,12 @@ func (s *AdapterTestSuite) TestSavePolicyClearPreviousData() {
 		_, err := s.e.RemovePolicy(p)
 		s.Require().NoError(err)
 	}
+	policies = s.e.GetGroupingPolicy()
+	policies = append(policies[:0:0], policies...)
+	for _, p := range policies {
+		_, err := s.e.RemoveGroupingPolicy(p)
+		s.Require().NoError(err)
+	}
 	s.assertPolicy(
 		[][]string{},
 		s.e.GetPolicy(),