code: public void registerArchetypeTree (String treeReference, BehaviorTree<?> archetypeTree) {
  		if (archetypeTree == null) {
  			throw new IllegalArgumentException("The registered archetype must not be null.");
  		}
  		repository.put(treeReference, archetypeTree);
  	}
docs: Registers the {@link BehaviorTree} archetypeTree with the specified reference. Existing archetypes in the repository with
  the same treeReference will be replaced.
  @param treeReference the tree identifier, typically a path.
  @param archetypeTree the archetype tree.
  @throws IllegalArgumentException if the archetypeTree is null