Merge branch '5.2' into 5.x

* 5.2:
  bug #40427 [Console] Stop accepting ints as InputOption defaults
  Fix fingerprint when context is not serializable
  Fix `ConstraintViolation#getMessageTemplate()` to always return `string`

Author: derrabus

ConstraintViolation.php

@@ -100,7 +100,7 @@ public function __toString()
      */
     public function getMessageTemplate()
     {
-        return $this->messageTemplate;
+        return (string) $this->messageTemplate;
     }
 
     /**

Tests/ConstraintViolationTest.php

@@ -171,4 +171,19 @@ public function testRetrievedPropertyPathIsAStringEvenIfNotSet()
             ))->getPropertyPath()
         );
     }
+
+    public function testRetrievedMessageTemplateIsAStringEvenIfNotSet()
+    {
+        self::assertSame(
+            '',
+            (new ConstraintViolation(
+                'irrelevant',
+                null,
+                [],
+                'irrelevant',
+                'irrelevant',
+                null
+            ))->getMessageTemplate()
+        );
+    }
 }