Theme hook webform_handler_PLUGIN_ID_summary not found

Problem/Motivation

When implementing a Webform handler without overriding the getSummary() method or adding a webform_handler_PLUGIN_ID_summary theme hook, the following warning is logged:

Theme hook webform_handler_PLUGIN_ID_summary not found.

This has been bothering me for a while when writing custom/contrib Webform handlers. Not every handler needs a summary, usually only handlers with configuration.

Proposed resolution

Check if the theme hook exists before using it.