I wholeheartedly agree with your comment. The core is that OP created something of value, in his own time. So there should be a value exchange of some sort.
The employer might be under the impression that all the terms in the employment contract they pulled off FreeLegalTemplates.net are enforceable when they aren't. Going to a lawyer first gives you the ammunition to politely point out that you are in fact the one in the right here.