# File lib/grape/middleware/versioner/header.rb, line 32
        def before
          strict_header_checks if strict?

          if media_type || env[Grape::Env::GRAPE_ALLOWED_METHODS]
            media_type_header_handler
          elsif headers_contain_wrong_vendor?
            fail_with_invalid_accept_header!('API vendor not found.')
          elsif headers_contain_wrong_version?
            fail_with_invalid_version_header!('API version not found.')
          end
        end