class Rubocop::Cop::Style::FavorUnlessOverNegatedIf

without else are considered.
Checks for uses of if with a negated condition. Only ifs

def error_message
  'Favor unless (or control flow or) over if for negative conditions.'
end

def on_if(node)
  return unless node.loc.respond_to?(:keyword)
  return if node.loc.keyword.is?('elsif')
  check(node)
end