global

def inspect = 'Grape::Util::Translation::MISSING' }.new.freeze

the default before returning it.
identifiable in debug output and immune to backends that call .to_s on
value). Using a named class rather than plain Object.new makes it
Sentinel returned by I18n when a key is missing (passed as the default: 
def inspect = 'Grape::Util::Translation::MISSING' }.new.freeze