[ML] Hide partition_scores field if empty (elastic/x-pack-elasticsearch#1189)

Original commit: elastic/x-pack-elasticsearch@5dec266e0d

plugin/src/main/java/org/elasticsearch/xpack/ml/job/results/Bucket.java

@@ -162,14 +162,16 @@ public class Bucket extends ToXContentToBytes implements Writeable {
         builder.field(BUCKET_SPAN.getPreferredName(), bucketSpan);
         builder.field(INITIAL_ANOMALY_SCORE.getPreferredName(), initialAnomalyScore);
         builder.field(RECORD_COUNT.getPreferredName(), recordCount);
-        if (!records.isEmpty()) {
+        if (records.isEmpty() == false) {
             builder.field(RECORDS.getPreferredName(), records);
         }
         builder.field(EVENT_COUNT.getPreferredName(), eventCount);
         builder.field(IS_INTERIM.getPreferredName(), isInterim);
         builder.field(BUCKET_INFLUENCERS.getPreferredName(), bucketInfluencers);
         builder.field(PROCESSING_TIME_MS.getPreferredName(), processingTimeMs);
-        builder.field(PARTITION_SCORES.getPreferredName(), partitionScores);
+        if (partitionScores.isEmpty() == false) {
+            builder.field(PARTITION_SCORES.getPreferredName(), partitionScores);
+        }
         builder.field(Result.RESULT_TYPE.getPreferredName(), RESULT_TYPE_VALUE);
         builder.endObject();
         return builder;

plugin/src/test/resources/rest-api-spec/test/ml/jobs_get_result_buckets.yaml

@@ -70,6 +70,8 @@ setup:
   - match: { buckets.1.timestamp: 1470009600000 }
   - match: { buckets.1.job_id: farequote}
   - match: { buckets.1.result_type: bucket}
+  - is_false: buckets.0.partition_scores
+  - is_false: buckets.1.partition_scores
 
 ---
 "Test get buckets given exclude_interim is false":