It will work faster without the if statement.
If statements make your CPU chace 80% of the positive branch, which leads to cache misses when going for negative branches.
Whenever you are able to get rid of a "if" statement then you made a huge improvement.
Considering your case where you don't have the positive branch the usual case scenario (usual case scenario for a positive branch is something like if (argument!=NULL) ), then you should have a significant performance gain.
The performance gain also varies accourding to CPU type (RISC or CISC).