NullPointerException when using setJsonVariable with null value

[jaboehri]

Description

In API v2, using Variables#setJsonVariable using a null value e.g. setJsonVariable("foo", null) throws a NullPointerException because VariablesImpl uses getClass() on the serialized object which breaks if the object is null.

Effected DSF Version

• 2.1.0
• 2.0.1
• 2.0.2
• 2.0.0

To Reproduce

Call setJsonVariable in a process plugin with a variable name of your choice and a null value.

Expected Behavior

Set the variable to null, don't throw a NullPointerException.

Logs

BPE:

WARN pool-6-thread-1 - AbstractErrorHandler.handleException(68) | Process dsfdev_ping:4:64a6671d-791f-11f1-af47-76c45e579722 has fatal error in step SavePongServiceTask:1bbb9b12-79e4-11f1-8645-ba4df22d5e8b for service task https://ttp/fhir/Task/e2f34a84-479a-4a0d-93e7-19ad57339158, reason: java.lang.NullPointerException - Cannot invoke "Object.getClass()" because "json" is null