Fix consistency in sessions not found exceptions

Author: jderusse

CHANGELOG.md

@@ -4,6 +4,7 @@ CHANGELOG
 5.3
 ---
 
+ * Calling `Request::getSession()` when there is no available session throws a `SessionNotFoundException`
  * Add the `RequestStack::getSession` method
  * Deprecate the `NamespacedAttributeBag` class
  * added `ResponseFormatSame` PHPUnit constraint

Request.php

@@ -13,6 +13,7 @@
 
 use Symfony\Component\HttpFoundation\Exception\ConflictingHeadersException;
 use Symfony\Component\HttpFoundation\Exception\JsonException;
+use Symfony\Component\HttpFoundation\Exception\SessionNotFoundException;
 use Symfony\Component\HttpFoundation\Exception\SuspiciousOperationException;
 use Symfony\Component\HttpFoundation\Session\SessionInterface;
 
@@ -735,7 +736,7 @@ public function getSession()
         }
 
         if (null === $session) {
-            throw new \BadMethodCallException('Session has not been set.');
+            throw new SessionNotFoundException('Session has not been set.');
         }
 
         return $session;