Document isReadable/getValue with

Author: chalasr

components/property_access/introduction.rst

@@ -46,7 +46,12 @@ method. This is done using the index notation that is used in PHP::
     var_dump($accessor->getValue($person, '[first_name]')); // 'Wouter'
     var_dump($accessor->getValue($person, '[age]')); // null
 
-As you can see, the method will return ``null`` if the index does not exists.
+.. caution::
+
+    As you can see, the method will return ``null`` if the index does not exists.
+    To make it throws an exception in case of invalid index, set the first argument
+    :method:`PropertyAccess::createPropertyAccessor<Symfony\\Component\\PropertyAccess\\PropertyAccess::createPropertyAccessor()>`
+    to true, e.g. ``PropertyAccess::createPropertyAccessor(true)``.
 
 You can also use multi dimensional arrays::
 
@@ -321,6 +326,13 @@ instead::
         // ...
     }
 
+.. caution::
+
+    Calling :method:`PropertyAccess::createPropertyAccessor<Symfony\\Component\\PropertyAccess\\PropertyAccess::createPropertyAccessor()>`
+    with an array for an invalid index would always return ``true``. To make it returns ``false``, set the first argument
+    :method:`PropertyAccess::createPropertyAccessor<Symfony\\Component\\PropertyAccess\\PropertyAccess::createPropertyAccessor()>`
+    to true, e.g. ``PropertyAccess::createPropertyAccessor(true)``.
+
 The same is possible for :method:`PropertyAccessor::setValue<Symfony\\Component\\PropertyAccess\\PropertyAccessor::setValue>`:
 Call the
 :method:`PropertyAccessor::isWritable<Symfony\\Component\\PropertyAccess\\PropertyAccessor::isWritable>`