Unexpected absent return value in convert_to_hypergraph

[leotrs]

I'd expect convert.convert_to_hypergraph to ALWAYS return a hypergraph. However:

In [2]: xgi.convert_to_hypergraph([{1,2,3},{2,3},{3,4}])

In [3]: xgi.convert_to_hypergraph([{1,2,3},{2,3},{3,4}], create_using=xgi.Hypergraph)

In [4]: xgi.convert_to_hypergraph([{1,2,3},{2,3},{3,4}], create_using=xgi.Hypergraph())

In [5]: xgi.convert_to_hypergraph(None)
Out[5]: <xgi.classes.hypergraph.Hypergraph at 0x7faf87067190>

Only the last one has a return value! This is because convert_to_hypergraph is designed to be used alongside create_using, and populate the passed in hypergraph in-place. This is far from ideal, I'd say. We should redesign the interface of this and other functions in the convert module.

[maximelucas]

Not ideal indeed, good catch.
+1 for making these convert functions more consistent.