Get URL to collection logo.

        :returns: Path to community logo.
        :rtype: str

def logo_url(self):
        """Get URL to collection logo.

        :returns: Path to community logo.
        :rtype: str
        """
        if self.logo_ext:
            return '/api/files/{bucket}/{key}'.format(
                bucket=current_app.config['COMMUNITIES_BUCKET_UUID'],
                key='{0}/logo.{1}'.format(self.id, self.logo_ext),
            )
        return None