TASK: Docs and readability of Node::getProperty

When seeing code like

```
$this->properties[$propertyName]
```

i always assume it will throw if the key not exits.
In our case the property collection will just return null instead.

To make this more obvious
A: i like to add a nullish-coalescing
or
B: use offsetGet similar to hasProperty uses offsetExist

Also the doc comment was adjusted, as its actually the same from the old cr and we dont have those funny content object dingsis anymore

Neos.ContentRepository.Core/Classes/Projection/ContentGraph/Node.php

@@ -65,7 +65,7 @@ public function __construct(
          *
          * To read the serialized properties, call properties->serialized().
          *
-         * @return PropertyCollectionInterface Property values, indexed by their name
+         * @var PropertyCollectionInterface Property values, indexed by their name
          */
         public readonly PropertyCollectionInterface $properties,
         public readonly ?NodeName $nodeName,
@@ -74,18 +74,15 @@ public function __construct(
     }
 
     /**
-     * Returns the specified property.
-     *
-     * If the node has a content object attached, the property will be fetched
-     * there if it is gettable.
+     * Returns the specified property, or null if it does not exist (or was set to null -> unset)
      *
      * @param string $propertyName Name of the property
      * @return mixed value of the property
      * @api
      */
     public function getProperty(string $propertyName): mixed
     {
-        return $this->properties[$propertyName];
+        return $this->properties->offsetGet($propertyName);
     }
 
     /**

Neos.ContentRepository.Core/Classes/Projection/ContentGraph/PropertyCollection.php

@@ -55,9 +55,11 @@ public function offsetGet($offset): mixed
     {
         if (!isset($this->deserializedPropertyValuesRuntimeCache[$offset])) {
             $serializedProperty = $this->serializedPropertyValues->getProperty($offset);
-            $this->deserializedPropertyValuesRuntimeCache[$offset] = $serializedProperty === null
-                ? null
-                : $this->propertyConverter->deserializePropertyValue($serializedProperty);
+            if ($serializedProperty === null) {
+                return null;
+            }
+            $this->deserializedPropertyValuesRuntimeCache[$offset] =
+                $this->propertyConverter->deserializePropertyValue($serializedProperty);
         }
 
         return $this->deserializedPropertyValuesRuntimeCache[$offset];