```ruby
require 'simple_enum/accessors/accessor'

module SimpleEnum
  module Accessors
    class WhinyAccessor < Accessor
      def write(object, key)
        raise ArgumentError, "#{key} is not a valid enum value for #{enum}" if key && !enum.include?(key)
        super
      end
    end
  end
end
```

Allow empty Strings when using `whiny` Accessor.
user
```ruby
require 'simple_enum/accessors/accessor'

module SimpleEnum
  module Accessors
    class WhinyAccessor < Accessor
      def write(object, key)
        raise ArgumentError, "#{key} is not a valid enum value for #{enum}" if key.present? && !enum.include?(key)
        super
      end
    end
  end
end
```
assistant