Better error messages while debugging Redmine and Redmine plugins

Anyone new to Ruby and/or Rails might have hard time setting up servers and/or following various tutorials on how to configure and which tools/servers to use for development.

This post considers that you have already somehow figured out a good environment and started devleoping/debugging, but stumbled upon non-descriptive error messages, like this one, for example:

Let's try patching Redmine to support better error gem

1. Apply my patch from following issue:

2. Run bundle install

3. Restart Redmine (see section in my book about restarting redmine)

And after running rails s with same error, you should get a better error message looking like this: