@classmethod
def merge_duplicate_headers(cls, headers, key):
    """
        HTTP allows multiple values for the same header name. Most WSGI implementations
        merge these values using a comma as separator (this has been confirmed for wsgiref,
        werkzeug, gunicorn and uwsgi). Other implementations may use containers like
        multidict to store headers and have APIs to iterate over all values for a given key.

        This method is provided as a hook for framework integrations to provide their own
        TraceParent implementation. The implementation should return a single string. Multiple
        values for the same key should be merged using a comma as separator.

        :param headers: a dict-like header object
        :param key: header name
        :return: a single string value or None
        """
    return headers.get(key)
