Iterating over children of a DataSnapshot throws exception

When I try to iterate over the children in a DataSnapshot it throws a RangeError. This is the code that I have:

  Map<String, Object> mapOfMaps(DataSnapshot snapshot) {
    Map<String, Object> map = <String, Object>{};

    for (var child in snapshot.children) {
      if (child.children.isNotEmpty) {
        map[child.key!] = mapOfMaps(child);
      } else {
        map[child.key!] = child.value!;
      }
    }

    return map;
  }

There are 7 children but the exception says: RangeError (index): Invalid value: Not in inclusive range 0..6: -1. Why is it trying to start iterating at -1?

>Solution :

The issue is likely related to the fact that snapshot.children property is returning Iterable object which may not have a defined length.

To solve it try to check snapshot.children.isNotEmpty before iterating.
Or convert it directly to the list: snapshot.children.toList()