code: public boolean set(@Nullable CloseableReference<T> valueRef) {
      CloseableReference<T> clonedRef = CloseableReference.cloneOrNull(valueRef);
      return super.setResult(clonedRef, /* isLast */ true);
    }
docs: Sets the value of this data source.
  
  <p> This method will return {@code true} if the value was successfully set, or
  {@code false} if the data source has already been set, failed or closed.
  
  <p> Passed CloseableReference is cloned, caller of this method still owns passed reference
  after the method returns.
  
  @param valueRef closeable reference to the value the data source should hold.
  @return true if the value was successfully set.