Merge pull request #13579 from Automattic/vkarpov15/gh-13531

fix(model): avoid TypeError if insertMany() fails with error that does not have `writeErrors` property

Author: vkarpov15

lib/model.js

@@ -3234,16 +3234,19 @@ Model.$__insertMany = function(arr, options, callback) {
         }
 
         // `insertedDocs` is a Mongoose-specific property
+        const hasWriteErrors = error && error.writeErrors;
         const erroredIndexes = new Set((error && error.writeErrors || []).map(err => err.index));
 
-        for (let i = 0; i < error.writeErrors.length; ++i) {
-          const originalIndex = validDocIndexToOriginalIndex.get(error.writeErrors[i].index);
-          error.writeErrors[i] = {
-            ...error.writeErrors[i],
-            index: originalIndex
-          };
-          if (!ordered) {
-            results[originalIndex] = error.writeErrors[i];
+        if (error.writeErrors != null) {
+          for (let i = 0; i < error.writeErrors.length; ++i) {
+            const originalIndex = validDocIndexToOriginalIndex.get(error.writeErrors[i].index);
+            error.writeErrors[i] = {
+              ...error.writeErrors[i],
+              index: originalIndex
+            };
+            if (!ordered) {
+              results[originalIndex] = error.writeErrors[i];
+            }
           }
         }
 
@@ -3260,7 +3263,7 @@ Model.$__insertMany = function(arr, options, callback) {
         let firstErroredIndex = -1;
         error.insertedDocs = docAttributes.
           filter((doc, i) => {
-            const isErrored = erroredIndexes.has(i);
+            const isErrored = !hasWriteErrors || erroredIndexes.has(i);
 
             if (ordered) {
               if (firstErroredIndex > -1) {