How to reproduce:
- Generate a LogEvent with an Exception that has at least one cause (i.e. nested Exception)
- Use the standard JSON Layout to turn that LogEvent into JSON
- Using JsonLogEventParser to turn it back into a LogEvent
- Call getExtendedStackTraceAsString() on the ThrowableProxy associated with the deserialized LogEvent
- A NullPointerException will be thrown
I've attached a small example project to reproduce the error.