def __init__(self, content_id=None):
self._content_id = None<EOL>if content_id is not None:<EOL><INDENT>self.content_id = content_id<EOL><DEDENT>
Create a ContentId object

        :param content_id: The content id for the attachment.
                           This is used when the Disposition is set to "inline"
                           and the attachment is an image, allowing the file to
                           be displayed within the email body.
        :type content_id: string, optional