   {"Content-Type": " "},
        "",
        'setRequestHeader(" ") sends the string " "'
      )
      request(
        function _String() { return ""; },
        {"Content-Type": null},
        "null",
        'setRequestHeader(null) sends the string "null"'
      )
      request(
        function _String() { return ""; },
        {"Content-Type": undefined},
        "undefined",
        'setRequestHeader(undefined) sends the string "undefined"'
      )
      request(
        function _String() { return 