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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_header(self, name: str, value: _HeaderTypes) -> None: """Adds the given response header and value. Unlike `set_header`, `add_header` may be called multiple times to return multiple values for the same header. """

        self._headers.add(name, self._convert_header_value(value))