Follow Up Change Events Improvements

Author: Giorgio Franceschetti

example/manual/watch/watch_on_collection.dart

@@ -63,7 +63,8 @@ void main() async {
   /// As the stream does not end until it is closed, do not use .toList()
   /// or you will wait indefinitely
   var controller = stream.listen((changeEvent) {
-    Map fullDocument = changeEvent.fullDocument;
+    Map<String, dynamic> fullDocument =
+        changeEvent.fullDocument ?? <String, dynamic>{};
 
     print('Detected change for "custId" '
         '${fullDocument['custId']}: "${fullDocument['name']}"');

example/manual/watch/watch_on_collection_insert.dart

@@ -50,7 +50,8 @@ void main() async {
   /// As the stream does not end until it is closed, do not use .toList()
   /// or you will wait indefinitely
   var controller = stream.listen((changeEvent) {
-    Map fullDocument = changeEvent.fullDocument;
+    Map<String, dynamic> fullDocument =
+        changeEvent.fullDocument ?? <String, dynamic>{};
 
     print('Detected change for "custId" '
         '${fullDocument['custId']}: "${fullDocument['name']}"');

test/op_msg_read_operation_test.dart

@@ -1878,7 +1878,8 @@ db.runCommand(
 
       var aResult = 3;
       var controller = stream.listen((changeEvent) {
-        Map fullDocument = changeEvent.fullDocument;
+        Map<String, dynamic> fullDocument =
+            changeEvent.fullDocument ?? <String, dynamic>{};
 
         expect(fullDocument['a'], aResult++);