GraphiQL Explorer always show error at UserStandardAttributes and UserCustomAttributes variables

When putting the `UserStandardAttributes` and `UserCustomAttributes` in the "Variables" pane,
the type checking in GraphiQL always show error, although the request can run successfully.

This is very confusing for the user because the type checking is not reliable.


Reproduce the issue in the GraphiQL Explorer by placing UserStandardAttributes and UserCustomAttributes in the Variables pane and comparing the type-checking error with successful execution. Trace the Explorer's variable validation entry point; done means valid variables no longer show a type-checking error while the request continues to run successfully.

Written by the indexing model from the issue text.