Steps to reproduce the issue

Create and publish an instance of mod_tags_similar (Tags - Similar).

Expected result

If the current page has other items with similar tags then those items will show in the list. If not then an error message will show stating "No matching tags." ( MOD_TAGS_SIMILAR_NO_MATCHING_TAGS ).

Actual result

If the current page has no items with similar tags then nothing shows (no message).

System information (as much as possible)

Joomla 3.8.8

Additional comments

The issue is caused by lines 24 to 27 of modules/mod_tags_similar/mod_tags_similar.php.
These lines can be removed because the default template accounts for an empty list and shows the error instead.