Uninitialized type properties are silently discarded on array cast

Cf. <https://bugs.php.net/81629>.

language/types/array.xml

@@ -840,6 +840,8 @@ $error_descriptions[8] = "This is just an informal notice";
    private variables have the class name prepended to the variable
    name; protected variables have a '*' prepended to the variable name. These
    prepended values have <literal>NUL</literal> bytes on either side.
+   Uninitialized <link linkend="language.oop5.properties.typed-properties">typed properties</link>
+   are silently discarded.
   </para>
 
   <informalexample>

reference/classobj/functions/get-mangled-object-vars.xml

@@ -17,6 +17,8 @@
    exceptions: private variables have the class name prepended to the variable name,
    and protected variables have a <literal>*</literal> prepended to the variable name.
    These prepended values have <literal>NUL</literal> bytes on either side.
+   Uninitialized <link linkend="language.oop5.properties.typed-properties">typed properties</link>
+   are silently discarded.
   </para>
  </refsect1>