So for this exercise, is the assumption for the answer string to be all lowercase?

I use my answer string as "Treehouse" and found this following bug:

You have 4 tries left to solve: --------- Enter a letter: t You have 3 tries left to solve: --------- Enter a letter: T t has already been guessed. Please try again. Enter a letter: r You have 3 tries left to solve: -r------- Enter a letter: e You have 3 tries left to solve: -ree----e Enter a letter: h You have 3 tries left to solve: -reeh---e Enter a letter: o You have 3 tries left to solve: -reeho--e Enter a letter: u You have 3 tries left to solve: -reehou-e Enter a letter: s You have 3 tries left to solve: -reehouse Enter a letter: t

When I guessed t it's rejecting it, but when I entered T, it's also rejected since it was considered as a guess. Might be something to be put on the bug report.