Add assert to Table to check for rows with null children (#61457)

packages/flutter/lib/src/widgets/table.dart

@@ -113,6 +113,15 @@ class Table extends RenderObjectWidget {
   }) : assert(children != null),
        assert(defaultColumnWidth != null),
        assert(defaultVerticalAlignment != null),
+       assert(() {
+         if (children.any((TableRow row) => row.children == null)) {
+           throw FlutterError(
+             'One of the rows of the table had null children.\n'
+             'The children property of TableRow must not be null.'
+           );
+         }
+         return true;
+       }()),
        assert(() {
          if (children.any((TableRow row) => row.children.any((Widget cell) => cell == null))) {
            throw FlutterError(

packages/flutter/test/widgets/table_test.dart

@@ -956,5 +956,29 @@ void main() {
     },
   );
 
+  testWidgets(
+    'Table widget requires all TableRows to have non-null children',
+    (WidgetTester tester) async {
+      FlutterError error;
+      try {
+        await tester.pumpWidget(
+          Directionality(
+            textDirection: TextDirection.ltr,
+            child: Table(
+              children: const <TableRow>[
+                TableRow(children: <Widget>[Text('Some Text')]),
+                TableRow(),
+              ],
+            ),
+          ),
+        );
+      } on FlutterError catch (e) {
+        error = e;
+      } finally {
+        expect(error, isNotNull);
+        expect(error.toStringDeep(), contains('The children property of TableRow must not be null.'));
+      }
+  });
+
   // TODO(ianh): Test handling of TableCell object
 }