WrongContainedType in registry while upgrading from Plone 4 to 5

[agitator]

Traceback (innermost last):
  Module ZPublisher.Publish, line 138, in publish
  Module ZPublisher.mapply, line 77, in mapply
  Module Products.PDBDebugMode.runcall, line 70, in pdb_runcall
  Module ZPublisher.Publish, line 48, in call_object
  Module Products.GenericSetup.tool, line 579, in manage_importAllSteps
  Module Products.GenericSetup.tool, line 388, in runAllImportStepsFromProfile
   - __traceback_info__: profile-bda.plone.shop:default
  Module Products.GenericSetup.tool, line 1433, in _runImportStepsFromContext
  Module Products.GenericSetup.tool, line 1245, in _doRunImportStep
   - __traceback_info__: plone.app.registry
  Module plone.app.registry.exportimport.handler, line 70, in importRegistry
  Module plone.app.registry.exportimport.handler, line 125, in importDocument
  Module plone.app.registry.exportimport.handler, line 412, in importRecords
   - __traceback_info__: records name: bda.plone.shop.interfaces.IShopShippingSettings
  Module plone.app.registry.exportimport.handler, line 329, in importRecord
   - __traceback_info__: record name: bda.plone.shop.interfaces.IShopShippingSettings.available_shipping_methods
  Module plone.registry.record, line 82, in _set_value
  Module zope.schema._bootstrapfields, line 183, in validate
  Module zope.schema._field, line 527, in _validate
WrongContainedType: ([WrongType(u'default_shipping', <type 'str'>, ''), WrongType(u'cash_and_carry', <type 'str'>, '')], 'value')

Removing purge="false" or setting it to true did work as workaround
https://github.com/bluedynamics/bda.plone.shop/blob/master/src/bda/plone/shop/profiles/base/registry.xml#L39
also in https://github.com/bluedynamics/bda.plone.shop/blob/master/src/bda/plone/shop/profiles/base/registry.xml#L74