Optional streams act as though they are required.

Describe the bug

Thanks for this library.

I may not fully understand the meaning of optional streams as it is not well documented. However, I would expect the first data request to be initiated without waiting for an optional stream to emit. Right now it seems that the optional streams must emit some value before the first data request will occur.

Adding the following operator to connect() in datasource-stream.ts does make the data source work as I would expect it to.

before

      optional.length
        ? merge(...optional).pipe(scan(this.reducePartials, {} as Partial<T>))
        : of({} as Partial<T>),

after

optional.length
        ? merge(...optional).pipe(
            startWith({}),
            scan(this.reducePartials, {} as Partial<T>),
          )
        : of({} as Partial<T>),

Minimal Reproduction

I don't have a fully reproducible example right now but I can create one at some point if it will help.

A simple data source with the following stream added

    this.addStream({
      name: 'filter',
      stream: form.valueChanges,
      optional: true,
    });

Expected behavior

The data source should automatically process the first data request.

Screenshots

If applicable, add screenshots to help explain your problem.

Your Environment

Angular Version:

Anything else relevant?

matheo / angular