Validation Response cannot be Deserialised when answer key is null

[jsharkey13]

If a question attempt inadvertantly gets saved with an answer key that is null ; it cannot be deserialised again afterwards and leads to a null pointer exception every time a user opens the menu on their account.

It would be nice if we could either deserialise correctly or silently skip the invalid attempt? I have prevented the invalid response from being persisted again - so this may be a 'wontfix' . . .

Caused by: java.lang.NullPointerException
	at uk.ac.cam.cl.dtg.segue.dao.users.QuestionValidationResponseDeserializer.deserialize(QuestionValidationResponseDeserializer.java:84)
	at uk.ac.cam.cl.dtg.segue.dao.users.QuestionValidationResponseDeserializer.deserialize(QuestionValidationResponseDeserializer.java:44)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3051)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2146)
	at uk.ac.cam.cl.dtg.segue.quiz.PgQuestionAttempts.getQuestionAttempts(PgQuestionAttempts.java:162)
	at uk.ac.cam.cl.dtg.segue.api.managers.QuestionManager.getQuestionAttemptsByUser(QuestionManager.java:317)