URL to a new form

After updating to Chronoforms 8.0.51, I'm getting the following error in a field with a button to open a new form:

Warning: Undefined array key "id" in ..... administrator\components\com_chronoforms8\pages\chronoforms\views\field_button\output.php on line 54

This seems to be related to the URL: {path:root}/index.php/benutzer-eingaben/

What is the correct setting? Thanks for your help.

There's obviously a bug, which I've temporarily fixed with this workaround. 

File: Output PHP

echo '<a class="nui button '.$field["class"].$field["code"].'"'.' href="'.Chrono::r(Chrono::addUrlParam($url, $params)).'">'.$icon.$field["label"].'</a>';
// echo '<a class="nui button '.$field["class"].'" id="'.$field["id"].'" '.$field["code"].' href="'.Chrono::r(Chrono::addUrlParam($url, $params)).'">'.$icon.$field["label"].'</a>';