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

Using `Object.create(null)` when creating objects for the anomaly
results table.

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;
       }