Unable to coalesce on del(...)

[pikeas]

.ts = del(.timestamp) ?? .ts ?? %docker_logs.timestamp

This fails with:

│ .ts = del(.timestamp) ?? .ts ?? %journald.timestamp
│       ^^^^^^^^^^^^^^^ -- --- this expression never resolves
│       │               │
│       │               remove this error coalescing operation
│       this expression can't fail

From https://vector.dev/docs/reference/vrl/expressions/:

expression | The expression (operand) can be any expression.

The error indicates that only errors may be coalesced, whereas the docs suggest that coalescing can be used generally, to select the first non-null value.

The intent here is to have a consistent timestamp field name after parse_logfmt is applied to heterogenous apps with different log outputs.

[pikeas]

.ts = .timestamp ?? .ts also fails.

If this is WAI, please update the docs to clarify that coalescing can only be used for error handling.

expression | The expression (operand) can be any fallible expression (eg, parse_json() but not parse_json!()) that returns an error.