src/main/java/com/github/oxo42/stateless4j/StateConfiguration.java
public StateConfiguration<S, T> permitInternalIf(T trigger, FuncBoolean guard, Action action) {
        assert guard != null : GUARD_IS_NULL;
        assert action != null : ACTION_IS_NULL;
        representation.addTriggerBehaviour(new InternalTriggerBehaviour<S, T>(
                trigger, guard, action));
        return this;
    }
public StateConfiguration<S, T> permitInternalIf(T trigger, FuncBoolean guard, Action action) {
        assert guard != null : GUARD_IS_NULL;
        assert action != null : ACTION_IS_NULL;
        representation.addTriggerBehaviour(new InternalTriggerBehaviour<S, T>(
                trigger, guard, action));
        return this;
    }
Accept the specified trigger, execute action and stay in state
<p>
Applies to the current state only. No exit or entry actions will be
executed and the state will not change. The only thing that happens is
the execution of a given action.
<p>
The action is only executed if the given guard returns true. Otherwise
this transition will not be taken into account (so it does not count
as 'ignore', then).

@param trigger The accepted trigger
@param guard   Function that must return true in order for the trigger to be accepted
@param action  The action to be performed
@return The receiver