Safe select operator

[jam01]

It would be useful to have a selector notation that was null safe. Perhaps ?. as Kotlin has https://kotlinlang.org/docs/null-safety.html#safe-calls

{x: 1}?.y

would return null instead of throwing an error

Edit: realized that this is something that would have to be added to jsonnet first. I've opened the same item on that project.

[lihaoyi-databricks]

Gonna close this for now; we can re-open it when it's implemented upstream