Next, I will talk about the theory of the empty nature (sunnata) of all dhammas, which follows from the notion of Dependent Origination. It holds that all dhammas are simply the cooperation of relative causes and conditions. Therefore, there is no substance in them. In other words, all dhammas are nothing but the phenomena of cooperation of causes and conditions. Apart from phenomena there is no noumenon as their dominator. 

When I said previously that “There is no ego within all dhammas”, I was speaking of the absence of “self” (atta) of human beings. And now I add the absence of self of all dhammas. The former is to deny self in human beings, and prove “non-substantiality in beings”, while the latter is to deny the self in dhammas, and prove “non-substantiality in dhammas”. (From Essentials of Buddhism: Questions and Answers)