Automator doesn’t have any control actions, so any comparisons you will need to do yourself. This is easy though, you can run a script after your Filter Paragraphs action to quit the workflow if the result is empty - for example, add a Run AppleScript action after the filter/before the new message and paste the following script into it:

on****run {input, parameters}

ifinputis {} then****error-128_— cancel on empty input list_