After an array is emitted, what to do with
last values. By default, the last value is kept.
If 'undefined' is used, undefined is used until
source emits again.
Default: 'last'
finalValue: "undefined" | "last"
If we continue synchronisation when a source is done (via onSourceDone:'allow'),
what source should be returned for a completed source?
After an array is emitted, what to do with last values. By default, the last value is kept. If 'undefined' is used, undefined is used until source emits again.
Default: 'last'