Custom Field Display ByKey error

When I add:

{$record->customFieldDisplayByKey('required-experience', 'listing')|raw}

To html widget, it causes:

Error: Call to a member function customFieldDisplayByKey() on null (0)
#-----/public_html/applications/cms/widgets/Codemirror.php(140): IPS\Theme\content_widget_b3027e()