The message means that despite invoking strict, you haven't declared @params before using it (or upon first use). You can make the message 'go away' by declaring my @params before your Line 6. (NB: that makes it global; something generally wise to avoid.)

Knowing nothing about Muscle, I have mention that making the message 'go away' may not be the actual solution to your problem. So heed the suggestion above from the Anonymous Monk, as the reference may tell you otherwise.