HttpHeaders.opIndexAssign
void opIndexAssign(string value, string name)Map-like assignment: headers["name"] = "value".
void opIndexAssign(typeof(null), string name)Map-like delete: headers["name"] = null.
void opIndexAssign(string value, string name)Map-like assignment: headers["name"] = "value".
void opIndexAssign(typeof(null), string name)Map-like delete: headers["name"] = null.