code: private void addCallback(BeanMessageID type, Callback<?> callback) {
          List<Callback<?>> callbacks = beanCallbacks.get(type);
          if (callbacks == null) {
              callbacks = new ArrayList<>(16);
              beanCallbacks.put(type, callbacks);
          }
          callbacks.add(callback);
      }
docs: Add a callback for a Bean message type.
  
  @param type      The {@link com.punchthrough.bean.sdk.internal.BeanMessageID} the callback
  will answer to
  @param callback  The callback to store