Archive sources fails due to non-existing ref in submodule repository

2019-04-16 14:14:42,287.287 DEBUG:storage.py:336: Creating archive: /home/citest/ci-working-dir/storage/qt/qtwebengine/320c7316b75be22112cb4802187c3873c9934eab/sources_unix.tar.gz
2019-04-16 14:14:42,615.615 ERROR:workitem.py:550: Unable to create source archives for workitem qt/qtwebengine/9b0ade0d4fa7bb7d23a13f63a77d1a3887308883/LinuxUbuntu_18_04x86_64LinuxUbuntu_18_04x86_64GCCqt
ci-linux-Ubuntu-18.04-x86_64-6c467fLicenseCheck_TestOnly/2ac096fea56b84fe8a94e2c27f3c8863b78eca49/Test:
ESC[31mTraceback (most recent call last):
  File "/home/citest/tqtc-coin-ci/src/workitem.py", line 541, in _createSourceArchive
    await asyncio.wait_for(createArchiveCoro, timeout=self.waitingForSourceArchiveCreatedTimeout, loop=self.loop)
  File "/usr/lib/python3.6/asyncio/tasks.py", line 358, in wait_for
    return fut.result()
  File "/home/citest/tqtc-coin-ci/src/storage.py", line 415, in createSourceArchives
    await asyncio.gather(*(storage.ensureSourceArchive(*args) for args in toExecute), loop=loop)
  File "/home/citest/tqtc-coin-ci/src/storage.py", line 357, in ensureSourceArchive
    includeSubModules=not excludeSubModules) for windowsLineFeeds in (False, True)))
  File "/home/citest/tqtc-coin-ci/src/storage.py", line 341, in _archive
    await archiveCoro
  File "/home/citest/tqtc-coin-ci/src/repositorymanager.py", line 388, in archive
    targetArchive, revision, prefix="", extraGitOptions=extraGitOptions)
  File "/home/citest/tqtc-coin-ci/src/repositorymanager.py", line 365, in archiveSubmodules
    sub_archives = await asyncio.gather(*(archive_submodule(*args) for args in sub_archives_args))
  File "/home/citest/tqtc-coin-ci/src/repositorymanager.py", line 358, in archive_submodule
    await ash.git("--git-dir=" + clonePath, "--no-pager", "archive", "--prefix=" + modulePrefix, sha1, output=submoduleArchive.name)
  File "/home/citest/tqtc-coin-ci/src/ash.py", line 146, in __call__
    raise sh.ErrorReturnCode_128(" ".join(processed_args), stdout, stderr)
sh.ErrorReturnCode_128:   RAN: git --git-dir=/home/citest/git-repos/qt-project/qt/qtwebengine/modules/src/3rdparty --no-pager archive --prefix=src/3rdparty/ 3d95374cb8de20b3e15538f1ecb5b78bf9d1cdcb --output=/tmp/coin-src-archive
-a3kq05333d9537  STDOUT:
  STDERR:
fatal: not a tree object
ESC[0m

2019-04-16 14:14:35,360.360 INFO:repositorymanager.py:352: Fetching +refs/heads/*:refs/heads/* of submodule repo /home/citest/git-repos/qt-project/qt/qtwebengine/modules/src/3rdparty