For some reason when I tried to check if $_FILES['myVarName'] was empty() or !isset() or array_key_exists(), it always came back that the file was indeed in the superglobal, even when nothing was uploaded.
I wonder if this is a result of enctype="multipart/form-data".
Anyways, I solved my issue by checking to make sure that $_FILES['myVarName']['size'] > 0