Add whitespace check for required validator (#779)

* Add whitespace check for required validator

* Format code_page file

Author: Ted-chiptech

example/lib/code_page.dart

@@ -36,4 +36,3 @@ class _CodePageState extends State<CodePage> {
     );
   }
 }
-

lib/src/form_builder_validators.dart

@@ -28,7 +28,7 @@ class FormBuilderValidators {
   }) {
     return (T? valueCandidate) {
       if (valueCandidate == null ||
-          (valueCandidate is String && valueCandidate.isEmpty) ||
+          (valueCandidate is String && valueCandidate.trim().isEmpty) ||
           (valueCandidate is Iterable && valueCandidate.isEmpty) ||
           (valueCandidate is Map && valueCandidate.isEmpty)) {
         return errorText ??

test/form_builder_validators_test.dart

@@ -1,8 +1,8 @@
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter_form_builder/flutter_form_builder.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
 import 'package:flutter_test/flutter_test.dart';
-import 'package:flutter_form_builder/flutter_form_builder.dart';
 
 /// Test Harness for running Validations
 Future<void> testValidations(
@@ -69,6 +69,7 @@ void main() {
             // Fail
             expect(validatorString(null), isNotNull);
             expect(validatorString(''), isNotNull);
+            expect(validatorString(' '), isNotNull);
 
             final validatorList =
                 FormBuilderValidators.required<List<int>>(context);