code: @SafeVarargs
  	public final TaskExecutor<T> addObservers(TaskObserver<T>... observers) {
  		if(observers != null) {
  			for(TaskObserver<T> observer : observers) {
  				this.observers.add(observer);
  			}
  		}
  		return this;
  	}
docs: Adds task observers to the set of registered observers.
  
  @param observers
  an list of observers that will be notified of the several phases in a
  task execution life cycle.
  @return
  the object itself, to enable method chaining.