handle error when deleting non existing key

internal/rpc/rpc.go

@@ -140,6 +140,9 @@ func (t *Query) Delete(np *VaultService, success *bool) error {
 	err := val.Delete(np.Service)
 	if err != nil {
 		*success = false
+		if err == storage.ErrNotFound {
+			return nil
+		}
 		return err
 	}