defaultIfEmpty

Substitutes a value if the source completes without emitting.

Signature

defaultIfEmpty(defaultValue: R): OperatorFunction

What it does

It tracks whether any value arrived. If source completes empty, it emits defaultValue and completes the stream.

When to use

Empty search results, a fallback for filters, safe aggregation after first/last/find.

See also

isEmpty, throwIfEmpty, EMPTY