On my slow machine this causes rescue mode failure only halt working, this is because it takes to much time to enumerate (with this function checks). I should have used the CableConnected function but since the F4 doesn't have that function it would make this branch be flagged as non compiling.
I have opened #1026 to fix the issue with compiling with that function but further work is needed to fix it for F4.
FWIW this is not an issue with this particular branch, current next BL doesn't work for me (rescue) on both F1 and F3 (the ones I can test).