Remove pretend-nils

[mvz]

• Don't pretend console self is nil
• Use #empty? instead of #nil? to distinguish empty commands
• Simplify implementation of have_exit_status matcher

Summary

Remove methods that make non-nil objects pretend they are nil.

Details

Removes implementations of #nil? that returned true for classes that are not NilClass; Also updates the #inspect method for self in the Aruba console not to return the string "nil".

Motivation and Context

Having objects respond with true to the #nil? message is super-confusing for humans, machines and cyborgs.

How Has This Been Tested?

I ran the specs and cukes.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Internal change (refactoring, test improvements, developer experience or update of dependencies)

Checklist:

• I've added tests for my code
• My change requires a change to the documentation.
• I have updated the documentation accordingly.