[7.17] [ML] Fixing issue with empty object creation (#186821) (#186900)

# Backport

This will backport the following commits from `main` to `7.17`:
- [[ML] Fixing issue with empty object creation
(#186821)](#186821)

<!--- Backport version: 9.4.3 -->

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<!--BACKPORT [{"author":{"name":"James
Gowdy","email":"jgowdy@elastic.co"},"sourceCommit":{"committedDate":"2024-06-25T15:23:25Z","message":"[ML]
Fixing issue with empty object creation (#186821)\n\nUsing
`Object.create(null)` when creating objects for the anomaly\r\nresults
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with empty object
creation","number":186821,"url":"#186821
Fixing issue with empty object creation (#186821)\n\nUsing
`Object.create(null)` when creating objects for the anomaly\r\nresults
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Fixing issue with empty object creation (#186821)\n\nUsing
`Object.create(null)` when creating objects for the anomaly\r\nresults
table.","sha":"8e76b0b113089c793e4dba77610f90540ec9b8da"}},{"branch":"7.17","label":"v7.17.23","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"},{"branch":"8.14","label":"v8.14.2","branchLabelMappingKey":"^v(\\d+).(\\d+).\\d+$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: James Gowdy <jgowdy@elastic.co>

x-pack/plugins/ml/server/models/results_service/build_anomaly_table_items.js

@@ -125,35 +125,40 @@ function aggregateAnomalies(anomalyRecords, interval, dateFormatTz) {
     return [];
   }
 
-  const aggregatedData = {};
+  const aggregatedData = Object.create(null);
   anomalyRecords.forEach((record) => {
     // Use moment.js to get start of interval.
     const roundedTime =
       dateFormatTz !== undefined
         ? moment(record.timestamp).tz(dateFormatTz).startOf(interval).valueOf()
         : moment(record.timestamp).startOf(interval).valueOf();
     if (aggregatedData[roundedTime] === undefined) {
-      aggregatedData[roundedTime] = {};
+      aggregatedData[roundedTime] = Object.create(null);
     }
 
     // Aggregate by job, then detectorIndex.
     const jobId = record.job_id;
     const jobsAtTime = aggregatedData[roundedTime];
-    if (jobsAtTime[jobId] === undefined) {
-      jobsAtTime[jobId] = {};
+    if (jobsAtTime[jobId] === undefined || Object.hasOwn(jobsAtTime, jobId) === false) {
+      jobsAtTime[jobId] = Object.create(null);
     }
 
     // Aggregate by detector - default to function_description if no description available.
     const detectorIndex = record.detector_index;
+    if (typeof detectorIndex !== 'number') {
+      return;
+    }
     const detectorsForJob = jobsAtTime[jobId];
     if (detectorsForJob[detectorIndex] === undefined) {
-      detectorsForJob[detectorIndex] = {};
+      detectorsForJob[detectorIndex] = Object.create(null);
     }
 
     // Now add an object for the anomaly with the highest anomaly score per entity.
     // For the choice of entity, look in order for byField, overField, partitionField.
     // If no by/over/partition, default to an empty String.
-    const entitiesForDetector = detectorsForJob[detectorIndex];
+    const entitiesForDetector = Object.hasOwn(detectorsForJob, detectorIndex)
+      ? detectorsForJob[detectorIndex]
+      : Object.create(null);
 
     // TODO - are we worried about different byFields having the same
     // value e.g. host=server1 and machine=server1?
@@ -163,7 +168,7 @@ function aggregateAnomalies(anomalyRecords, interval, dateFormatTz) {
     }
     if (entitiesForDetector[entity] === undefined) {
       entitiesForDetector[entity] = record;
-    } else {
+    } else if (Object.hasOwn(entitiesForDetector, entity)) {
       if (record.record_score > entitiesForDetector[entity].record_score) {
         entitiesForDetector[entity] = record;
       }