Some cleanup changes.

--
MOS_MIGRATED_REVID=87821306
diff --git a/src/main/java/com/google/devtools/build/lib/vfs/UnionFileSystem.java b/src/main/java/com/google/devtools/build/lib/vfs/UnionFileSystem.java
index b349b53..d2d9c00 100644
--- a/src/main/java/com/google/devtools/build/lib/vfs/UnionFileSystem.java
+++ b/src/main/java/com/google/devtools/build/lib/vfs/UnionFileSystem.java
@@ -88,7 +88,7 @@
         "please use the rootFileSystem argument instead.");
 
     this.readOnly = readOnly;
-    this.pathDelegate = new StringTrie<FileSystem>();
+    this.pathDelegate = new StringTrie<>();
 
     for (Map.Entry<PathFragment, FileSystem> prefix : prefixMapping.entrySet()) {
       FileSystem delegate = prefix.getValue();