code: public boolean tryRef(T t)
      {
          Ref<T> ref = t.tryRef();
          if (ref == null)
              return false;
          ref = references.put(t, ref);
          if (ref != null)
              ref.release(); // release dup
          return true;
      }
docs: Attempt to take a reference to the provided object; if it has already been released, null will be returned
  @param t object to acquire a reference to
  @return true iff success