This prevents logging of messages where no category is specified as part of JLog::add.
Add JLog::add("This shouldn't be here", JLog::INFO); to your template's index.php file.
Before this patched the logging statement This shouldn't be here will be included in the messages block. According to the docs this should ONLY be displayed when the jerror category is set. (https://docs.joomla.org/Using_JLog)
After this patch the message will not be displayed. Logging entries will only be logged when category is included. For example:
JLog::add("This should be here", JLog::INFO,"jerror");