.push() chokes on empty word?

[helixbass]

Hi, sorry I'm just posting this quickly as I ran into this, I can probably re-create/add more details if you want

I believe that I'm accidentally currently pushing an empty word (eg "") when using map::TrieBuilder to construct a map::Trie

And then it looks like that is causing a panic at this line: https://github.com/laysakura/trie-rs/blob/9fdacbb/src/internal_data_structure/naive_trie/naive_trie_impl.rs#L50

This is just a guess right now as I looked at the source code of that method since it is maybe currently assuming that it goes through the for loop at least once (and conceptually it I'm guessing makes no sense to try and push an empty word into a trie)

[shanecelis]

Thank you. Should be easy to test and easy to fix.