It can happen that TransactionFactory::createTransaction() fails to create a transaction object because an unsuitable type is passed
(like BadType) and returns a null pointer.
The calling instances (Transaction::addObjectChange, Transaction::addObjectDel, Transaction::addObjectNew, Transaction::addOrRemoveProperty)
do not check for a null pointer and thus cause a segmentation fault by dereferencing it.
To fix the issue change the above methods to explicitly handle a null pointer.
This fixes issue 21095.
Note: In this case it's caused by the class ViewProviderFace which on purpose isn't added to the type system so that its type will be BadType.
1886bcda00