minor #14151 [Workflow] pass arguments to getMetadata method (lubo13)

This PR was submitted for the 5.1 branch but it was squashed and merged into the 4.4 branch instead.

Discussion
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[Workflow] pass arguments to getMetadata method

By my opinion and the code in a trait, I saw that to the getMetadata method we should pass two arguments. But the first should be the key from metadata and the second should be null (for workflow's metadata), string (for place's metadata) or instance of Transition (for transition's metadata)

Commits
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8b36b82 [Workflow] pass arguments to getMetadata method

Author: javiereguiluz

workflow.rst

@@ -858,14 +858,14 @@ Then you can access this metadata in your controller as follows::
 
 There is a ``getMetadata()`` method that works with all kinds of metadata::
 
-    // pass no arguments to getMetadata() to get "workflow metadata"
-    $title = $workflow->getMetadataStore()->getMetadata()['title'];
+    // pass a string (the key of workflow metadata) to getMetadata() to get "workflow metadata" by key
+    $title = $workflow->getMetadataStore()->getMetadata('title');
 
-    // pass a string (the place name) to getMetadata() to get "place metadata"
-    $maxNumOfWords = $workflow->getMetadataStore()->getMetadata('draft')['max_num_of_words'];
+    // pass two arguments: a string (the key of place metadata) and a string (the place name) to getMetadata() to get "place metadata" by key
+    $maxNumOfWords = $workflow->getMetadataStore()->getMetadata('max_num_of_words', 'draft');
 
-    // pass a Transition object to getMetadata() to get "transition metadata"
-    $priority = $workflow->getMetadataStore()->getMetadata($aTransition)['priority'];
+    // pass two arguments: a string (the key of transition metadata) and a Transition object to getMetadata() to get "transition metadata" by key
+    $priority = $workflow->getMetadataStore()->getMetadata('priority', $aTransition);
 
 In a :ref:`flash message <flash-messages>` in your controller::