Directed/undirected expected degree hypergraphs: "illegal" edges?

[arashbm]

Take the following example:

d = ret.random_directed_expected_degree_sequence_hypergraph[ret.int64]([(2, 2)]*200000, [(5,5)]*80000, random_state=state)

It produces an edge with zero vertices, and many edges with only in- or out-verts. Similarly, the undirected variant creates one zero-degree edge and many one-degree edges. What should we do about them?

Other libraries leave them be, although some produce many zero-degree edges that are distinguished by an edge id.