Don't use data pointers in form render arrays

src/JsonForms/Definition/Control/ArrayControlDefinition.php

@@ -21,6 +21,8 @@
 
 namespace Drupal\json_forms\JsonForms\Definition\Control;
 
+use Drupal\json_forms\Util\ConvertUtil;
+
 final class ArrayControlDefinition extends ControlDefinition {
 
   public function getItems(): ?\stdClass {
@@ -35,27 +37,27 @@ public function getPrefixItems(): ?array {
   }
 
   public function getMaxItems(): ?int {
-    return $this->propertySchema->maxItems ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->maxItems ?? NULL);
   }
 
   public function getMinItems(): ?int {
-    return $this->propertySchema->minItems ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->minItems ?? NULL);
   }
 
   public function getUniqueItems(): ?bool {
-    return $this->propertySchema->uniqueItems ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->uniqueItems ?? NULL);
   }
 
   public function getContains(): ?\stdClass {
     return $this->propertySchema->contains ?? NULL;
   }
 
   public function getMaxContains(): ?int {
-    return $this->propertySchema->maxContains ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->maxContains ?? NULL);
   }
 
   public function getMinContains(): ?int {
-    return $this->propertySchema->minContains ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->minContains ?? NULL);
   }
 
 }

src/JsonForms/Definition/Control/NumberControlDefinition.php

@@ -21,33 +21,35 @@
 
 namespace Drupal\json_forms\JsonForms\Definition\Control;
 
+use Drupal\json_forms\Util\ConvertUtil;
+
 class NumberControlDefinition extends ControlDefinition {
 
   public function getMultipleOf(): ?int {
-    return $this->propertySchema->multipleOf ?? NULL;
+    return ConvertUtil::stdClassToNull($this->getpropertySchema->multipleOf ?? NULL);
   }
 
   public function getMaximum(): ?int {
-    return $this->propertySchema->maximum ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->maximum ?? NULL);
   }
 
   public function getExclusiveMaximum(): ?int {
-    return $this->propertySchema->exclusiveMaximum ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->exclusiveMaximum ?? NULL);
   }
 
   public function getMinimum(): ?int {
-    return $this->propertySchema->minimum ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->minimum ?? NULL);
   }
 
   public function getExclusiveMinimum(): ?int {
-    return $this->propertySchema->exclusiveMinimum ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->exclusiveMinimum ?? NULL);
   }
 
   /**
    * @return int|null Not a standardized property.
    */
   public function getPrecision(): ?int {
-    return $this->propertySchema->precision ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->precision ?? NULL);
   }
 
 }

src/JsonForms/Definition/Control/ObjectControlDefinition.php

@@ -21,14 +21,16 @@
 
 namespace Drupal\json_forms\JsonForms\Definition\Control;
 
+use Drupal\json_forms\Util\ConvertUtil;
+
 final class ObjectControlDefinition extends ControlDefinition {
 
   public function getMaxProperties(): ?int {
-    return $this->propertySchema->maxProperties ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->maxProperties ?? NULL);
   }
 
   public function getMinProperties(): ?int {
-    return $this->propertySchema->minProperties ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->minProperties ?? NULL);
   }
 
   /**
@@ -42,7 +44,7 @@ public function getProperties(): \stdClass {
    * @return array<string>|null
    */
   public function getRequired(): ?array {
-    return $this->propertySchema->required ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->required ?? NULL);
   }
 
   public function getDependentRequired(): ?\stdClass {

src/JsonForms/Definition/Control/StringControlDefinition.php

@@ -21,18 +21,20 @@
 
 namespace Drupal\json_forms\JsonForms\Definition\Control;
 
+use Drupal\json_forms\Util\ConvertUtil;
+
 class StringControlDefinition extends ControlDefinition {
 
   public function getMaxLength(): ?int {
-    return $this->propertySchema->maxLength ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->maxLength ?? NULL);
   }
 
   public function getMinLength(): ?int {
-    return $this->propertySchema->minLength ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->minLength ?? NULL);
   }
 
   public function getPattern(): ?string {
-    return $this->propertySchema->pattern ?? NULL;
+    return ConvertUtil::stdClassToNull($this->propertySchema->pattern ?? NULL);
   }
 
 }

src/Util/ConvertUtil.php

@@ -0,0 +1,39 @@
+<?php
+
+/*
+ * Copyright (C) 2023 SYSTOPIA GmbH
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace Drupal\json_forms\Util;
+
+final class ConvertUtil {
+
+  /**
+   * Returns NULL if the value is an \stdClass, otherwise the value itself.
+   *
+   * This method might be used for constraints in form render arrays such that
+   * no data pointer (defined in \stdClass object) will be used there.
+   *
+   * @param mixed $value
+   *
+   * @return mixed|null
+   */
+  public static function stdClassToNull($value) {
+    return $value instanceof \stdClass ? NULL : $value;
+  }
+
+}