'How to get sum of firestore document values using fold? Flutter

body: StreamBuilder<QuerySnapshot>(
      stream: record,
      builder:
          (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
          ..........

          ..........
        final totalIncome =
            snapshot.data?.docs.fold<double>(0, (previousValue, element) {
          return previousValue + (element['incomeAmount'] ?? 0.0);
        }) as double;

     ...........
     ...........

This works if a field exists. If there is no field in firestore this gives an error field does not exist within the DocumentSnapshotPlatform

How can I make it work something like

element?['incomeAmount']

or if there is no field return 0?

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'How to get sum of firestore document values using fold? Flutter

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