Nikita Kozlov writes:

I was reading the source code of the pua_mi module and I think I have found some wrong check in mi_func.c (checking str.s == 0 instead of str.len == 0).

it may be that in those cases the two tests are equivalent, i.e., if string is empty, .s does not point to anything, i.e., its value is 0.

-- juha