Error in SkeletalMeshMerge.cpp -- what is the correct behavior?

Right around this point in Engine/Private/SkeletalMeshMerge.cpp

It says
checkf(false, TEXT("Invalid number of UV sets. Must be between 0 and 4") );\

However, the switch immediately above it only has cases for 1,2,3,4, it does not include 0.

What is the correct behavior for 0? Should it be processed same as 1-4, differently from 1-4, or should it be an error and the error message updated to say 1-4?