I have an agent that is nested in another agent. This nested agent has a function that calls the annylogic probability distribution functions(pdfs) such as gamma(), lognormal(), etc. However I keep getting a nullPointerException if I call these pdfs inside the nested agent. I am realising this is because the nested agent cannot access the default randomNumberGenerator. Is there a way I can access the defaultRandomNumberGenerator within the nested agent as well or is the only solution to create a new generator for each nested agent?
The error is because your agent is outside the model hierarchy of agents.
This is not good practice; there should very rarely be a need to have 'floating' agents outside the model hierarchy; they can always be inside an agent population somewhere.
In the rare cases that there are strong design reasons to do so (or if you use plain Java classes and thus have Java objects which by definition are not Agents and are therefore outside the agent hierarchy), just give them a parameter (field in the case of a Java class) that points to some agent that is in the model hierarchy (typically their 'generator'), and then you can call all 'required-to-be-in-model-hierarchy' functions via that parameter. (That is, you are delegating all such calls to an agent instance which can call them.)
e.g., the nested agent type (let's say Thing) has parameter agentRef of type Agent set by whoever creates it; for example
Thing t = new Thing(this);
Then, within Thing, you use code such as agentRef.normal(1,10).