StreamBuilder's Firebase query appears and disappears instantly

Question

I am trying to query a Stream where the document should have 'UretimKurulum' in 'unit' array and the 'date' should be equal or greater than today's date.

While streaming this query I do get the correct results that I want for a brief seconds and then it says 'No Data Available'.

Below is the actual code:

  final FirebaseFirestore _db = FirebaseFirestore.instance;

  final DateTime _now = DateTime.now();
  final String val = 'UretimKurulum';

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<QuerySnapshot<Object>>(
      stream: _db.collection('Schedule').where('date', isGreaterThanOrEqualTo: _now).where('unit', arrayContains: val).snapshots(),
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting) {
          return Center(child: LinearProgressIndicator());
        } else {
          if (!snapshot.hasData) {
            return Center(child: Text('No Data Available'));
          } else {
            return ListView.builder(
              itemCount: snapshot.data!.docs.length,
              itemBuilder: (context, index) {
                var docSnap = snapshot.data!.docs[index];
                return Text(docSnap.id);
              },
            );
          }
        }
      },
    );
  }
}

If I try to remove:

if (!snapshot.hasData) {
            return Center(child: Text('No Data Available'));
          }

I get the following error:

════════ Exception caught by widgets library ═══════════════════════════════════
The following TypeErrorImpl was thrown building StreamBuilder<QuerySnapshot<Object>>(dirty, state: _StreamBuilderBaseState<QuerySnapshot<Object>, AsyncSnapshot<QuerySnapshot<Object>>>#0508a):
Unexpected null value.

Answer 1

And indeed it was an indexing issue as @blaneyneil and myself stated previously.

The solution was to create a composite collection index from the Firebase Console and index the fields 'todoUnit' as Arrays and 'date' as Ascending.