adapt to upstream changes

Author: Hendrik Muhs

x-pack/plugin/ml-feature-index-builder/src/main/java/org/elasticsearch/xpack/ml/featureindexbuilder/job/AggregationConfig.java

@@ -15,7 +15,7 @@
 import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactories;
 import java.io.IOException;
-import java.util.List;
+import java.util.Collection;
 import java.util.Objects;
 
 /*
@@ -46,7 +46,7 @@ public void writeTo(StreamOutput out) throws IOException {
         aggregatorFactoryBuilder.writeTo(out);
     }
 
-    public List<AggregationBuilder> getAggregatorFactories() {
+    public Collection<AggregationBuilder> getAggregatorFactories() {
         return aggregatorFactoryBuilder.getAggregatorFactories();
     }
 

x-pack/plugin/ml-feature-index-builder/src/main/java/org/elasticsearch/xpack/ml/featureindexbuilder/job/FeatureIndexBuilderIndexer.java

@@ -69,7 +69,7 @@ protected IterationResult<Map<String, Object>> doProcess(SearchResponse searchRe
     private List<IndexRequest> processBuckets(CompositeAggregation agg) {
         // for now only 1 source supported
         String destinationFieldName = job.getConfig().getSourceConfig().getSources().get(0).name();
-        String aggName = job.getConfig().getAggregationConfig().getAggregatorFactories().get(0).getName();
+        String aggName = job.getConfig().getAggregationConfig().getAggregatorFactories().iterator().next().getName();
 
         return agg.getBuckets().stream().map(b -> {
             NumericMetricsAggregation.SingleValue aggResult = b.getAggregations().get(aggName);