minor #658 Changed "null" by "~" in yaml files (yceruto)

This PR was merged into the master branch.

Discussion
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Changed "null" by "~" in yaml files

According to:

* https://github.com/symfony/recipes/blob/master/symfony/framework-bundle/3.3/config/packages/test/framework.yaml#L2

* https://github.com/symfony/recipes/blob/master/symfony/framework-bundle/3.3/config/packages/framework.yaml#L6

* https://github.com/symfony/recipes/blob/master/symfony/routing/3.3/config/packages/routing.yaml#L3

Commits
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dd6e36e Changed null by ~ in yaml files

Author: javiereguiluz

config/packages/framework.yaml

@@ -36,6 +36,6 @@ framework:
         handler_id: session.handler.native_file
         save_path: '%kernel.project_dir%/var/sessions/%kernel.environment%'
 
-    trusted_hosts: null
+    trusted_hosts: ~
 
     validation: { enable_annotations: true }

config/packages/routing.yaml

@@ -1,3 +1,3 @@
 framework:
     router:
-        strict_requirements: null
+        strict_requirements: ~

config/packages/test/framework.yaml

@@ -1,4 +1,4 @@
 framework:
-    test: null
+    test: ~
     session:
         storage_id: session.storage.mock_file