code: private Node tryReduceReturn(Node n) {
      Node result = n.getFirstChild();
  
      if (result != null) {
        switch (result.getToken()) {
          case VOID:
            Node operand = result.getFirstChild();
            if (!mayHaveSideEffects(operand)) {
              n.removeFirstChild();
              reportChangeToEnclosingScope(n);
            }
            break;
          case NAME:
            String name = result.getString();
            if (name.equals("undefined")) {
              n.removeFirstChild();
              reportChangeToEnclosingScope(n);
            }
            break;
          default:
            break;
        }
      }
  
      return n;
    }
docs: Reduce "return undefined" or "return void 0" to simply "return".
  
  @return The original node, maybe simplified.