Modify deepSet() to allow appending to arrays

lib/www/client/source/src/lib/utils.js

@@ -175,11 +175,19 @@ function deepEqual (a, b) {
  * If a non-leaf property does not exist, this function
  * creates it as an empty object ({}) and keeps traversing.
  *
+ * The last member of `path` may be `null`, in which case,
+ * if the object pointed to by the next to last member is
+ * an array, an insert operation will take place.
+ *
  */
 function deepSet (obj, path, value) {
   const key = path.shift();
   if (!path.length) {
-    obj[key] = value;
+    if (key === null && Array.isArray(obj)) {
+      obj.push(value);
+    } else {
+      obj[key] = value;
+    }
   } else {
     if (!Object.hasOwn(obj, key)) {
       obj[key] = {};