[syntax] Inverse null coalescing operator

[dustbort]

I agree with this concept, but I have some specific reasoning about the operator names.

'maybe' operator to complement ?? operator

We simply need this, although the 'appropriate' syntax is &?. Using ?? for nullish coalescing was unfortunate: In proposing the nullish coalescing operator ??, there is not much discussion aside from a reference to C#, from which the ?? syntax was borrowed. However, this is shortsighted, since C# uses boolean logic, while ES uses truthy logic. We take advantage of the fact that ES && and || operators will return the actual value of the first operand when short-circuiting occurs, rather than tr…

It often happens that the key might be a nullish foreign key ID. The database allows nullable foreign keys, and the code will naturally deal with this. We're looking for an elegant syntax for a common case.

Also note that pipelines do not address composite keys, where we would either need this operator anyway or the pipeline needs to support arbitrary number of arguments in an equivalent manner, which I am unable to see, since that would be a tuple to start the pipeline, but we want to coalesce the arguments in this way.