We use a YAML nil `~` to provide a default of empty string.

In Ruby, an empty string is truthy. As a result, passed a value of "" or
"nil", these branches of the code will run.

As a result, we need to change the default values of the input to `""`
and check if the passed value is an empty string.

No parsing is done to the values passed in as args so these are just
strings. `"nil"` doesn't become `nil` and is truthy.

We want to make thse messages consistent and read in the positive.
"not empty" is harder to understand than "provided".

Also, let's match the description formats.

Let's use the same approach for matching the regex to make this file
easier future changes.

This approach uses ruby regex string interpolation, where you can turn a
string into a regex with interpolating it into a regex expression.

Let's skip retrieving the list of issue comments if none of the options
requiring them will be used.

This restores a previous optimization that was removed.