Error message should be more descriptive

[mcwebb]

Really like the module, many thanks for the work.

The only thing that would make it better would be if the error message thrown were a bit more descriptive. Currently it looks like an unexpected runtime error which confuses people who are not familiar with this module (see screenshot).

It would be better if the error was at least more descriptive and ideally it would mention exactly which variable was unavailable. Something like: Environment variable 'VAR_NAME' unavailable. maybe?