Merge branch '4.4' into 5.2

* 4.4:
  Fix incompatible implicit float-to-int conversions
  [Translation] Don't pass null to strtoupper()
  cs fix
  [DependencyInjection] Don't pass null to trim()
  Add return types to JsonSerializable implementations
  Fix Serializable deprecations triggered by token mocks
  Add missing security translations

Author: derrabus

Tests/JsonResponseTest.php

@@ -251,9 +251,6 @@ public function testSetContentJsonSerializeError()
     {
         $this->expectException(\Exception::class);
         $this->expectExceptionMessage('This error is expected');
-        if (!interface_exists(\JsonSerializable::class, false)) {
-            $this->markTestSkipped('JsonSerializable is required.');
-        }
 
         $serializable = new JsonSerializableObject();
 
@@ -299,12 +296,10 @@ public function testConstructorWithObjectWithoutToStringMethodThrowsAnException(
     }
 }
 
-if (interface_exists(\JsonSerializable::class, false)) {
-    class JsonSerializableObject implements \JsonSerializable
+class JsonSerializableObject implements \JsonSerializable
+{
+    public function jsonSerialize(): array
     {
-        public function jsonSerialize()
-        {
-            throw new \Exception('This error is expected');
-        }
+        throw new \Exception('This error is expected');
     }
 }