Fix error with empty object property

src/Drupal/FormGeneratorDrupal.php

@@ -49,7 +49,7 @@ public function doTransform($data, Context $context = NULL) {
    */
   public function getInputValidator() {
     // Validate the JSON-Schema input.
-    return new JsonSchemaFormValidator(new Validator());
+    return new JsonSchemaFormValidator(new Validator(), Constraint::CHECK_MODE_TYPE_CAST);
   }
 
   /**

src/Drupal/FormValidatorDrupal.php

@@ -7,6 +7,7 @@
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Render\Element;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
+use JsonSchema\Constraints\Constraint;
 use JsonSchema\Validator;
 use SchemaForms\ArrayToStdClass;
 use SchemaForms\RecursiveTypeCaster;
@@ -38,7 +39,10 @@ public static function validateWithSchema(array &$element, FormStateInterface $f
     }
     $validator = new Validator();
     // Validate the massaged data against the schema.
-    $num_errors = $validator->validate($data, $schema);
+    if ($data === null) {
+      $data = [];
+    }
+    $num_errors = $validator->validate($data, $schema, Constraint::CHECK_MODE_TYPE_CAST);
     if ($num_errors) {
       // Build the mappings of paths to form paths.
       $mappings = static::buildMappingsElementPaths($element, $element['#array_parents']);

src/JsonSchemaFormValidator.php

@@ -23,8 +23,7 @@ public function __construct(Validator $validator, $mode = NULL) {
    */
   public function isValid($data) {
     return parent::isValid($data)
-      && $data->type === 'object'
-      && (bool) $data->properties;
+      && $data->type === 'object';
   }
 
 }