A potential $\pi_t$ is a positive supermartingale with the condition that $\mathbb{E}[\pi_t]\rightarrow 0$ as $t \rightarrow 0$. What are the necessary/sufficient conditions for a potential to be of Class D, as defined by Meyer (so that Doob-Meyer decomposition applies)?

We say a cadlag supermatingale Z is of Class D if the collection $( Z_T : \textrm{T is a finite stopping time})$ is uniformly integrable.