[Serializer] Fix DataUriNormalizer docblock & composer suggest section

src/Symfony/Component/Serializer/Normalizer/DataUriNormalizer.php

@@ -32,7 +32,7 @@ class DataUriNormalizer implements NormalizerInterface, DenormalizerInterface
     ];
 
     /**
-     * @var MimeTypeGuesserInterface
+     * @var MimeTypeGuesserInterface|null
      */
     private $mimeTypeGuesser;
 

src/Symfony/Component/Serializer/composer.json

@@ -44,7 +44,7 @@
         "symfony/yaml": "For using the default YAML mapping loader.",
         "symfony/config": "For using the XML mapping loader.",
         "symfony/property-access": "For using the ObjectNormalizer.",
-        "symfony/http-foundation": "To use the DataUriNormalizer.",
+        "symfony/http-foundation": "For using a MIME type guesser within the DataUriNormalizer.",
         "doctrine/annotations": "For using the annotation mapping. You will also need doctrine/cache.",
         "doctrine/cache": "For using the default cached annotation reader and metadata cache."
     },