FIX Don't try to access private properties/methods

src/Core/CustomMethods.php

@@ -147,7 +147,13 @@ protected function registerExtraMethodCallback($name, $callback)
      */
     public function hasMethod($method)
     {
-        return method_exists($this, $method ?? '') || $this->getExtraMethodConfig($method);
+        return (method_exists($this, $method ?? '') && !$this->isPrivateMethod($method)) || $this->getExtraMethodConfig($method);
+    }
+
+    private function isPrivateMethod(string $method): bool
+    {
+        $reflectionMethod = new ReflectionMethod($this, $method);
+        return $reflectionMethod->isPrivate();
     }
 
     /**

src/View/ViewableData.php

@@ -7,7 +7,9 @@
 use InvalidArgumentException;
 use IteratorAggregate;
 use LogicException;
+use ReflectionMethod;
 use ReflectionObject;
+use ReflectionProperty;
 use SilverStripe\Core\ClassInfo;
 use SilverStripe\Core\Config\Config;
 use SilverStripe\Core\Config\Configurable;
@@ -111,7 +113,7 @@ public function __construct()
     public function __isset($property)
     {
         // getField() isn't a field-specific getter and shouldn't be treated as such
-        if (strtolower($property ?? '') !== 'field' && $this->hasMethod($method = "get$property")) {
+        if (strtolower($property ?? '') !== 'field' && $this->hasMethod("get$property")) {
             return true;
         }
         if ($this->hasField($property)) {
@@ -159,20 +161,13 @@ public function __set($property, $value)
         $this->objCacheClear();
         $method = "set$property";
 
-        if ($this->hasMethod($method) && !$this->isPrivate($this, $method)) {
+        if ($this->hasMethod($method)) {
             $this->$method($value);
         } else {
             $this->setField($property, $value);
         }
     }
 
-    private function isPrivate(object $class, string $method): bool
-    {
-        $class = new ReflectionObject($class);
-
-        return $class->getMethod($method)->isPrivate();
-    }
-
     /**
      * Set a failover object to attempt to get data from if it is not present on this object.
      *
@@ -207,7 +202,13 @@ public function getFailover()
      */
     public function hasField($field)
     {
-        return property_exists($this, $field) || isset($this->data[$field]);
+        return (property_exists($this, $field) && !$this->isPrivateProperty($field)) || isset($this->data[$field]);
+    }
+
+    private function isPrivateProperty(string $property): bool
+    {
+        $reflectionProperty = new ReflectionProperty($this, $property);
+        return $reflectionProperty->isPrivate();
     }
 
     /**