Merge branch '5.4' into 6.0

* 5.4:
  Update serializer.rst
  [Serializer] Documenting the new SKIP_UNINITIALIZED_VALUES option

Author: javiereguiluz

components/serializer.rst

@@ -1193,6 +1193,41 @@ to ``true``::
     $result = $normalizer->normalize($dummy, 'json', [AbstractObjectNormalizer::SKIP_NULL_VALUES => true]);
     // ['bar' => 'notNull']
 
+Skipping Uninitialized Properties
+---------------------------------
+
+In PHP, typed properties have an ``uninitialized`` state which is different
+from the default ``null`` of untyped properties. When you try to access a typed
+property before giving it an explicit value, you get an error.
+
+To avoid the Serializer throwing an error when serializing or normalizing an
+object with uninitialized properties, by default the object normalizer catches
+these errors and ignores such properties.
+
+You can disable this behavior by setting the ``AbstractObjectNormalizer::SKIP_UNINITIALIZED_VALUES``
+context option to ``false``::
+
+    class Dummy {
+        public string $foo = 'initialized';
+        public string $bar; // uninitialized
+    }
+
+    $normalizer = new ObjectNormalizer();
+    $result = $normalizer->normalize(new Dummy(), 'json', [AbstractObjectNormalizer::SKIP_UNINITIALIZED_VALUES => false]);
+    // throws Symfony\Component\PropertyAccess\Exception\UninitializedPropertyException as normalizer cannot read uninitialized properties
+
+.. note::
+
+    Calling ``PropertyNormalizer::normalize`` or ``GetSetMethodNormalizer::normalize``
+    with ``AbstractObjectNormalizer::SKIP_UNINITIALIZED_VALUES`` context option set
+    to ``false`` will throw an ``\Error`` instance if the given object has uninitialized
+    properties as the normalizer cannot read them (directly or via getter/isser methods).
+
+.. versionadded:: 5.4
+
+    The ``AbstractObjectNormalizer::SKIP_UNINITIALIZED_VALUES`` constant was
+    introduced in Symfony 5.4.
+
 .. _component-serializer-handling-circular-references:
 
 Collecting Type Errors While Denormalizing