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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 content_type(self, content_type):
 """Sets the content_type of this Notificant. The value of the Content-Type header of the webhook POST request. # noqa: E501 :param content_type: The content_type of this Notificant. # noqa: E501 :type: str """

        allowed_values = ["application/json", "text/html", "text/plain", "application/x-www-form-urlencoded", ""]  # noqa: E501
        if content_type not in allowed_values:
            raise ValueError(
                "Invalid value for `content_type` ({0}), must be one of {1}"  # noqa: E501
                .format(content_type, allowed_values)
            )

        self._content_type = content_type