Change error message for typo in helper's name

I've tried to make the error message more helpful, when helper name is misspelled. I created new type of error (MissingHelperModuleError) which is raised when expected constant is not loaded. I'd appreciate any feedback  about my solution.
Thank you @kaspth for your comments. But here is the problem:
We can't use safe_camelize or camelize because then const_missing from Dependencies module is called and that leads to that "circular dependency" error. It does not appear in tests but do in real apps.