Issue Summary

When you try to add a custom field with special characters or accents in its name to show in the "Filter Results" gadget on a dashboard, it doesn't consider the added custom field.

Steps to Reproduce

1. Add a "Filter Results" gadget to a dashboard;
2. Select to show a custom field with special characters:
   
3. Save it;
4. The custom field doesn't show in the gadget:
   

Expected Results

The gadget should show the custom field selected.

Actual Results

There is no error showing in the requests that the browser is doing and the custom field is not showing in the gadget results.

Workaround

For now, it would be necessary to remove the special character or accents from the custom field.