The only new JCTree node in java7, JCTypeUnion, is now supported by delombok.

src/delombok/lombok/delombok/PrettyCommentsPrinter.java

@@ -1495,8 +1495,13 @@ public class PrettyCommentsPrinter extends JCTree.Visitor {
 
     public void visitTree(JCTree tree) {
         try {
-            print("(UNKNOWN: " + tree + ")");
-            println();
+            if ("JCTypeUnion".equals(tree.getClass().getSimpleName())) {
+                print(tree.toString());
+                return;
+            } else {
+                print("(UNKNOWN: " + tree + ")");
+                println();
+            }
         } catch (IOException e) {
             throw new UncheckedIOException(e);
         }