added empty_edges keyword

[nwlandry]

A user reached out and asked if we could allow empty edges. I added the empty_edges as an optional keyword to opt-in to this behavior.

[codecov[bot]]

Codecov Report

Patch coverage: 88.88% and no project coverage change.

Comparison is base (591d681) 90.43% compared to head (9edd480) 90.43%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #354   +/-   ##
=======================================
  Coverage   90.43%   90.43%           
=======================================
  Files          41       41           
  Lines        3012     3012           
=======================================
  Hits         2724     2724           
  Misses        288      288           

Impacted Files	Coverage Δ
xgi/classes/hypergraph.py	86.03% <87.50%> (ø)
xgi/convert.py	95.61% <100.00%> (ø)

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[leotrs]

I believe at some point we allowed for empty edges and then decided not to support them. Is this the case? If so, does anyone remember why we decided not tu support them?

[maximelucas]

Is this the case?

I don't remember honestly. Do we know what the use-case would be?

[leotrs]

@nwlandry :)

[nwlandry]

I originally wanted to include them to represent physical rooms without people in them. One of my colleagues wanted to represent groups that xould have 0 members. Lastly, there are several existing inconsistencies in XGI mentioned in #403.

[leotrs]

Okay yeah that sounds like a legit use case. We could try to implement this and the wait and see what breaks.

One caveat is that we'd need a whole battery of tests (several dozens) to test for integration of different corners of the library with empty edges.

[nwlandry]

This PR is stale and so I'm closing this. I will work on re-opening this in the future.