* Don't raise NoMethodError when validating emoji settings
Cargo culted the unique cross model slug validator setup (which is why
value is called name here in the validatable).
Don't raise an error when validating a nil emoji, and assert nil and
empty string are permitted values.
This expects no non-emoji characters (so an empty string would be
permitted), and nil should be permitted.
I believe this might have been introduced by the string settings
cleaner (exchanging "" for nil in form inputs).
* Update app/validators/emoji_only_validator.rb
guard for value, and then validate value
