\Drupal\Core\TypedData\TypedData

.gitignore

+.idea/
+sites/default/files/
+sites/default/settings.php
+vendor/
+sites/simpletest/
+.ddev/config.yaml

core/lib/Drupal/Core/TypedData/TypedData.php

@@ -92,14 +92,14 @@ public function getDataDefinition() {
    * {@inheritdoc}
    */
   public function getValue() {
-    return $this->value;
+    return $this->get('value')->getValue();
   }
 
   /**
    * {@inheritdoc}
    */
   public function setValue($value, $notify = TRUE) {
-    $this->value = $value;
+    $this->set('value', $value);
     // Notify the parent of any changes.
     if ($notify && isset($this->parent)) {
       $this->parent->onChange($this->name);

core/phpstan-baseline.neon

@@ -982,11 +982,6 @@ parameters:
 			count: 1
 			path: lib/Drupal/Core/TypedData/ListDataDefinition.php
 
-		-
-			message: "#^Access to an undefined property Drupal\\\\Core\\\\TypedData\\\\TypedData\\:\\:\\$value\\.$#"
-			count: 2
-			path: lib/Drupal/Core/TypedData/TypedData.php
-
 		-
 			message: "#^Variable \\$cache_key in isset\\(\\) always exists and is not nullable\\.$#"
 			count: 1