According to this (and I've seen similar more detailed expositions in Tsouna's book), anger can stem from pain but be sustained by "the pleasure of revenge." One is acceptable and understandable, the other is "empty."
I know that you're putting the quotes around "empty" because you're referring to references in the texts. At some point I would like us to spend some closer time examining those texts because I sense that "empty" is conveying things in English of which I don't think Epicurus would have approved. (I think another example of such a term would be "vainglory" as used a few times on this and other forums.)
I find that I don't use the "empty" term myself very much or at all, and when I see it used it seems it's frequently being applied as a label of disapproval for reasons that don't seem to have much to do with Epicurean philosophy. Maybe I will stand to be corrected on that and if so I will learn something, but I question how this term can be reconciled with the "all pleasure is desirable" foundation, and the foundation that pleasure and pain are intrinsically desirable/undesirable in themselves.