A vec and a string are basically the same thing (a series of bytes)

In the context of vectors I prefer my APIs to return an empty set rather than an None-option. This makes handling it much easier because you can still iterate over it, it just has nothing.

This might involve the compiler making an allocation of an empty array but most of them (gcc, ghc) will now what you are doing and optimize the null check on the empty array to a bool check.