Validating a checkbox -- before

Register.dart

Widget get _buildAgreeToTermsField {
  // TODO 8: Wrap the Column with a FormField<bool>
  return Column(
    children: <Widget>[
      Row(
        children: <Widget>[
          Checkbox(
            value: _agree,
            onChanged: (bool val) => setState(() {
              _agree = val;
            }),
          ),
          const Text("I agree to the terms."),
        ],
      ),
    ],
  );
}