def set_default_subject(self, subject):
        """
        Sets the subject's location media URL as a link.
        It displays as the default subject on PFE.

        - **subject** can be a single :py:class:`.Subject` instance or a single
          subject ID.

        Examples::

            collection.set_default_subject(1234)
            collection.set_default_subject(Subject(1234))
        """
        if not (
            isinstance(subject, Subject)
            or isinstance(subject, (int, str,))
        ):
            raise TypeError
        if isinstance(subject, Subject):
            _subject_id = subject.id
        else:
            _subject_id = str(subject)

        self.http_post(
            '{}/links/default_subject'.format(self.id),
            json={'default_subject': _subject_id},
        )