catch if given atree does not exist

js/display_atree.js

@@ -5,6 +5,8 @@ function construct_AT(elem, tree) {
     document.getElementById("atree-active").innerHTML = ""; //reset all atree actives - should be done in a more general way later
     elem.innerHTML = ""; //reset the atree in the DOM
     
+    if (tree === undefined) {return false;}
+
     // add in the "Active" title to atree
     let active_row = document.createElement("div");
     active_row.classList.add("row", "item-title", "mx-auto", "justify-content-center");