'Retrieve the collection of imported issues via the API.
See also: https://gist.github.com/jonmagic/5282384165e0f86ef105
:param int number: (optional), number of imported issues to return.
Default: -1 returns all branches
:param since: (optional), Only imported issues after this date will
be returned. This can be a ``datetime`` instance, ISO8601
formatted date string, or a string formatted like so:
``2016-02-04`` i.e. ``%Y-%m-%d``
:param str etag: (optional), ETag from a previous request to the same
endpoint
:returns: generator of :class:`ImportedIssue <github3.repos.
issue_import.ImportedIssue>`'

@requires_auth
def imported_issues(self, number=(-1), since=None, etag=None):

    data = {u'since': timestamp_parameter(since)}
    self._remove_none(data)
    url = self._build_url(u'import/issues', base_url=self._api)
    return self._iter(int(number), url, ImportedIssue, etag=etag, params=data, headers=ImportedIssue.IMPORT_CUSTOM_HEADERS)
