domain_name_validator 0.5 marks a valid .ninja domain (and many others) as "Malformed TLD: Could not possibly match any valid TLD", because many tlds with more than 3 characters are not whitelisted in lib/domain_name_validator/validator.rb
A workaround is removing constant MAX_TLD_LENGTH after require with:
DomainNameValidator.send('remove_const', 'MAX_TLD_LENGTH')