Only in C, other languages don't use null-terminated strings. A C++ std::string can contain a '\0' as the first character but still not be empty (though of course C++ code can also use C strings).

But even if an empty string truly contains no data it will match at the very beginning, so it seems returning 0 is still consistent.

Depends on your string representation. It's not unreasonable for an empty string to have no internal buffer allocated meaning it wouldn't even have a NUL terminator!