@h4ck0r86 - the easy way to do this is to simply enter what you'd like printed when you have no results into the "Default display if no results" option (including nothing, if you want nothing printed in that case) and similarly play with the before/after related entry/each post settings. The "display code example" on the right side will help you taylor these settings to your needs.
If you require some PHP in your if block, you can use the function related_posts_exist() which returns true or false and then print related_posts() inside that code block. Remember if you decide to go this route to then turn off the "automatically display related posts" option.
Thanks for trying out YARPP!