[Translation] Fix handling of null messages in ArrayLoader

src/Symfony/Component/Translation/Loader/ArrayLoader.php

@@ -46,9 +46,11 @@ private function flatten(array $messages): array
         foreach ($messages as $key => $value) {
             if (\is_array($value)) {
                 foreach ($this->flatten($value) as $k => $v) {
-                    $result[$key.'.'.$k] = $v;
+                    if (null !== $v) {
+                        $result[$key.'.'.$k] = $v;
+                    }
                 }
-            } else {
+            } elseif (null !== $value) {
                 $result[$key] = $value;
             }
         }

src/Symfony/Component/Translation/Tests/Loader/YamlFileLoaderTest.php

@@ -30,6 +30,15 @@ public function testLoad()
         $this->assertEquals([new FileResource($resource)], $catalogue->getResources());
     }
 
+    public function testLoadNonStringMessages()
+    {
+        $loader = new YamlFileLoader();
+        $resource = __DIR__.'/../fixtures/non-string.yml';
+        $catalogue = $loader->load($resource, 'en', 'domain1');
+
+        $this->assertSame(['root.foo2' => '', 'root.bar' => 'bar'], $catalogue->all('domain1'));
+    }
+
     public function testLoadDoesNothingIfEmpty()
     {
         $loader = new YamlFileLoader();

src/Symfony/Component/Translation/Tests/fixtures/non-string.yml

@@ -0,0 +1,4 @@
+root:
+  foo1:
+  foo2: ''
+  bar: 'bar'