diff --git a/vendors/knockout/src/binding/defaultBindings/value.js b/vendors/knockout/src/binding/defaultBindings/value.js
index 64b23d3d5..af7535d23 100644
--- a/vendors/knockout/src/binding/defaultBindings/value.js
+++ b/vendors/knockout/src/binding/defaultBindings/value.js
@@ -35,7 +35,7 @@ ko.bindingHandlers['value'] = {
             // This is useful, for example, to catch "keydown" events after the browser has updated the control
             // (otherwise, ko.selectExtensions.readValue(this) will receive the control's value *before* the key event)
             var handler = valueUpdateHandler;
-            if (ko.utils.stringStartsWith(eventName, "after")) {
+            if ((eventName||'').startsWith("after")) {
                 handler = () => {
                     // The elementValueBeforeEvent variable is non-null *only* during the brief gap between
                     // a keyX event firing and the valueUpdateHandler running, which is scheduled to happen
diff --git a/vendors/knockout/src/utils.js b/vendors/knockout/src/utils.js
index 7623819c7..1c9807a4f 100644
--- a/vendors/knockout/src/utils.js
+++ b/vendors/knockout/src/utils.js
@@ -89,13 +89,6 @@ ko.utils = {
                 string.trim() :
                 string.toString().replace(/^[\s\xa0]+|[\s\xa0]+$/g, ''),
 
-    stringStartsWith: (string, startsWith) => {
-        string = string || "";
-        if (startsWith.length > string.length)
-            return false;
-        return string.substring(0, startsWith.length) === startsWith;
-    },
-
     domNodeIsContainedBy: (node, containedByNode) =>
         containedByNode.contains(node.nodeType !== 1 ? node.parentNode : node),