BasePart:SubtractAsync (and potentially BasePart:UnionAsync) can return nil despite developer documentation

[Agapurnis]

Relevant method documentation states that it will return an Instance (actually, an empty abstract extension of PartOperation, but that's irrelevant here)

• https://developer.roblox.com/en-us/api-reference/function/BasePart/UnionAsync
• https://developer.roblox.com/en-us/api-reference/function/BasePart/SubtractAsync

However, an official announcement and personal experience state that it can return nil in certain events.

The operations throw an exception if there was a problem in computing the result (too many triangles, unsupported part types, the usual). If the result is an empty mesh, they return nil. If everything went well, they return a PartOperation representing the computed result, which can be used in subsequent operations if necessary.

~ linearcomplex, New Roblox In-Game CSG API is now availabl, August 31, 2018

Emphasis (bold) mine.

This can be edited here, as overrides are already present.

[Dionysusnu]

This might be a case of #543, or might just be an oversight.

[Agapurnis]

This might be a case of #543, or might just be an oversight.

I would be fine if it were solved similar to #543, as if it were forgotten/omitted in the documentation and an issue hasn't been raised here before, it obviously isn't a huge issue. This only really happened because I was negating things improperly, and this took me down the wrong direction.

[osyrisrblx]

Was able to reproduce this with SubtractAsync, but not UnionAsync. I thought if I negated one of the parts first and then unioned them together it would, but union async seems to treat negative parts as normal parts.