minor #17799 [DependencyInjection] Update tags.rst (hbgamra)

This PR was submitted for the 6.2 branch but it was merged into the 5.4 branch instead.

Discussion
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[DependencyInjection] Update tags.rst

Optimize getTransport() function

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Commits
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a2df575 Update tags.rst

Author: javiereguiluz

service_container/tags.rst

@@ -405,11 +405,7 @@ To begin with, change the ``TransportChain`` class::
 
         public function getTransport($alias): ?\MailerTransport
         {
-            if (array_key_exists($alias, $this->transports)) {
-                return $this->transports[$alias];
-            }
-
-            return null;
+            return  return $this->transports[$alias] ?? null;
         }
     }