code: void attach(JCTree tree, Comment dc) {
          if (keepDocComments && dc != null) {
  //          System.out.println("doc comment = ");System.out.println(dc);//DEBUG
              docComments.putComment(tree, dc);
          }
      }
docs: Make an entry into docComments hashtable,
  provided flag keepDocComments is set and given doc comment is non-null.
  @param tree   The tree to be used as index in the hashtable
  @param dc     The doc comment to associate with the tree, or null.