Plone 5.2 Migration Error Website with pas.plugins.ldap

Hello,

i'm trying to migrate to Plone 5.2 right now using the @@plone-upgrade tool.
My website uses the pas.plugins.ldap Extension for authentication purposes, but after a dry-run i get following message:

Step pas.plugins.ldap.setup has an invalid import handler
Added BooleanIndex for field exclude_from_nav.
Indexing new indexes exclude_from_nav.
Cleaned up the toolset registry.
Upgrade aborted. Error:
Traceback (most recent call last):
File "/home/vm-server/Plone/buildout-cache/eggs/Products.CMFPlone-5.2.0-py2.7.egg/Products/CMFPlone/MigrationTool.py", line 291, in upgrade
step['step'].doStep(setup)
File "/home/vm-server/Plone/buildout-cache/eggs/Products.GenericSetup-2.0-py2.7.egg/Products/GenericSetup/upgrade.py", line 168, in doStep
self.handler(tool)
File "/home/vm-server/Plone/buildout-cache/eggs/plone.app.upgrade-2.0.27-py2.7.egg/plone/app/upgrade/v52/betas.py", line 110, in to52beta1
remove_interface_indexes_from_relations_catalog()
File "/home/vm-server/Plone/buildout-cache/eggs/plone.app.upgrade-2.0.27-py2.7.egg/plone/app/upgrade/v52/betas.py", line 72, in remove_interface_indexes_from_relations_catalog
catalog.unindex(rel)
File "/home/vm-server/Plone/buildout-cache/eggs/zc.relation-1.1.post2-py2.7.egg/zc/relation/catalog.py", line 564, in unindex
self.unindex_doc(self._relTools['dump'](rel, self, {}))
File "/home/vm-server/Plone/buildout-cache/eggs/z3c.relationfield-0.8.0-py2.7.egg/z3c/relationfield/index.py", line 42, in dump
return intids.getId(obj)
File "/home/vm-server/Plone/buildout-cache/eggs/five.intid-1.2.3-py2.7.egg/five/intid/intid.py", line 41, in getId
return z3IntIds.getId(self, ob)
File "/home/vm-server/Plone/buildout-cache/eggs/zope.intid-4.3.0-py2.7.egg/zope/intid/init.py", line 108, in getId
raise IntIdMissingError(ob)
IntIdMissingError: <z3c.relationfield.relation.RelationValue object at 0x7f31efd72050 oid 0x3540 in <Connection at 7f3212e0cdd0>>
End of upgrade path, main migration has finished.
The upgrade path did NOT reach current version.
Migration has failed
Dry run selected, transaction aborted

Any ideas, how I can sort that out?

Yours Sincerely

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