transform_keys

# File activesupport/lib/active_support/hash_with_indifferent_access.rb, line 340
    def transform_keys(hash = NOT_GIVEN, &block)
      return to_enum(:transform_keys) if NOT_GIVEN.equal?(hash) && !block_given?
      dup.tap { |h| h.transform_keys!(hash, &block) }
    end