protected T nullOrUndefined(long snap, Address address) {
		return null;
	}
Create the appropriate unit (possibly caching) when there is no view or space for the given
address's space

<p>
Views composing undefined units should generate (possibly delegating to a view) an undefined
unit. Others should leave this null.

@param snap the snap the client requested
@param address the address the client requested
@return the unit or null
Ghidra/Debug/Framework-TraceModeling/src/main/java/ghidra/trace/database/listing/AbstractBaseDBTraceCodeUnitsMemoryView.java