Unhelpfull error: NPE if a PlanningListVariable on a PlanningEntity is null

[ge0ffrey]

I have a Vehicle with a null List<Visit> visits and I get this error:

java.lang.NullPointerException: Cannot invoke "java.util.List.size()" because the return value of "ai.timefold.solver.core.impl.domain.variable.descriptor.ListVariableDescriptor.getListVariable(Object)" is null
	at ai.timefold.solver.core.impl.domain.variable.descriptor.ListVariableDescriptor.getListSize(ListVariableDescriptor.java:118)

To reproduce, take the vrp quickstart and create a Vehicle with a null visit list.

Ideally, the error message should point out that the visits field of Vehicle (id) is null.