Merge branch '5.3' into 5.4

* 5.3:
  [Process] intersect with getenv() in case-insensitive manner to get default envs
  [Serializer] fix support for lazy/unset properties
  Fix redundant type casts
  [Notifier] Fix AllMySms bridge body content
  Revert "[DoctrineBridge] add support for the JSON type"

Iterator/RecursiveDirectoryIterator.php

@@ -64,7 +64,7 @@ public function current()
         // the logic here avoids redoing the same work in all iterations
 
         if (null === $subPathname = $this->subPath) {
-            $subPathname = $this->subPath = (string) $this->getSubPath();
+            $subPathname = $this->subPath = $this->getSubPath();
         }
         if ('' !== $subPathname) {
             $subPathname .= $this->directorySeparator;