Fix: AXE-570 Fixed a11yEngineErrors being accessed on undefined

lib/core/public/load.js

@@ -42,7 +42,10 @@ function runCommand(data, keepalive, callback) {
           //a11y-engine iframe rules error merging logic
           const errors = a11yEngine.getErrors();
           if (Object.keys(errors).length !== 0) {
-            if (results[results.length - 1].a11yEngineErrors) {
+            if (
+              results.length > 0 &&
+              results[results.length - 1]?.a11yEngineErrors
+            ) {
               const error = results.pop();
               delete error.a11yEngineErrors;
               const mergedErrors = mergeErrors(error, errors);

lib/core/public/run-rules.js

@@ -67,7 +67,10 @@ export default function runRules(context, options, resolve, reject) {
       // after should only run once, so ensure we are in the top level window
       if (context.initiator) {
         // Return a11y-engine errors when at top level window
-        if (results[results.length - 1].a11yEngineErrors) {
+        if (
+          results.length > 0 &&
+          results[results.length - 1]?.a11yEngineErrors
+        ) {
           const error = results.pop();
           delete error.a11yEngineErrors;
           a11yEngine.mergeErrors(error);

lib/core/utils/merge-results.js

@@ -86,7 +86,7 @@ function mergeResults(frameResults, options) {
 
     const frameSpec = getFrameSpec(frameResult);
     // Extract existing errors and merge with new ones
-    if (results[results.length - 1].a11yEngineErrors) {
+    if (results.length > 0 && results[results.length - 1]?.a11yEngineErrors) {
       const error = results.pop();
       delete error.a11yEngineErrors;
       mergedErrors = mergeErrors(mergedErrors, error, frameSpec);