diff --git a/apps/emqx_authn/test/emqx_authn_schema_SUITE.erl b/apps/emqx_authn/test/emqx_authn_schema_SUITE.erl
index 7e67584ac..cd1c38d06 100644
--- a/apps/emqx_authn/test/emqx_authn_schema_SUITE.erl
+++ b/apps/emqx_authn/test/emqx_authn_schema_SUITE.erl
@@ -78,7 +78,8 @@ t_check_schema(_Config) ->
     ).
 
 t_union_member_selector(_) ->
-    ?assertMatch(#{authentication := undefined}, check(undefined)),
+    %% default value for authentication
+    ?assertMatch(#{authentication := []}, check(undefined)),
     C1 = #{<<"backend">> => <<"built_in_database">>},
     ?assertThrow(
         #{