Fixing bug in addErrorMessages method

[algm]

I fixed a minor bug in the addErrorsMessages method in which the type variable was undefined.

[andrewhathaway]

Sorry for being picky, but this one I think should be done a little differently in the sense that the var/let keyword should be place inside of the loops "parameters", as such. IE:

for (let prop in obj) { ... }

Just to keep it clean, and how its usually approached. Good spot!

[algm]

I moved the let definition as you suggested, thanks for the feedback!