code: private void validateNoCollapse(Node n, JSDocInfo info) {
      if (n.isFromExterns()) {
        if (info != null && info.isNoCollapse()) {
          // @nocollapse has no effect in externs
          reportMisplaced(n, "nocollapse", "This JSDoc has no effect in externs.");
        }
        return;
      }
      if (!NodeUtil.isPrototypePropertyDeclaration(n.getParent())) {
        return;
      }
      JSDocInfo jsdoc = n.getJSDocInfo();
      if (jsdoc != null && jsdoc.isNoCollapse()) {
        reportMisplaced(n, "nocollapse", "This JSDoc has no effect on prototype properties.");
      }
    }
docs: Warns when nocollapse annotations are present on nodes
  which are not eligible for property collapsing.