Steps to reproduce the issue

create new custom module, write just the following<img > then save; please note there is space after img, where if don't put space like <img> will works normally.

Expected result

save the module normally as stay on administrator view "Backend"

Actual result

404 error page appear

System information (as much as possible)

Joomla 3.8.8

Additional comments

This issue appear after upgrade to 3.8.8, where thare are many custom modules were working normally before, now once try just save them without any change, 404 error page appear.