code: public static <T> Collection<T> addAllNotNull(Collection<T> to, Collection<? extends T> what) {
          Collection<T> data = safeCollection(to);
          if (!isEmpty(what)) {
              for (T t : what) {
                  if (t != null) {
                      data.add(t);
                  }
              }
          }
          return data;
      }
docs: NULL safe addAll()