Aggregations: Pass extended bounds into HistogramAggregator when creating an unmapped aggregator

This fixes an issue where if the field for the aggregation was unmapped the extended bounds would get dropped and the resulting buckets would not cover the extended bounds requested.

Closes #14735

core/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/HistogramAggregator.java

@@ -173,7 +173,7 @@ public class HistogramAggregator extends BucketsAggregator {
         @Override
         protected Aggregator createUnmapped(AggregationContext aggregationContext, Aggregator parent, List<PipelineAggregator> pipelineAggregators,
                 Map<String, Object> metaData) throws IOException {
-            return new HistogramAggregator(name, factories, rounding, order, keyed, minDocCount, null, null, config.formatter(),
+            return new HistogramAggregator(name, factories, rounding, order, keyed, minDocCount, extendedBounds, null, config.formatter(),
                     histogramFactory, aggregationContext, parent, pipelineAggregators, metaData);
         }
 

plugins/lang-groovy/src/test/java/org/elasticsearch/messy/tests/HistogramTests.java

@@ -892,6 +892,39 @@ public class HistogramTests extends ESIntegTestCase {
         }
     }
 
+    public void testPartiallyUnmappedWithExtendedBounds() throws Exception {
+        SearchResponse response = client()
+                .prepareSearch("idx", "idx_unmapped")
+                .addAggregation(
+                        histogram("histo").field(SINGLE_VALUED_FIELD_NAME).interval(interval)
+                                .extendedBounds((long) -1 * 2 * interval, (long) valueCounts.length * interval)).execute().actionGet();
+
+        assertSearchResponse(response);
+
+        Histogram histo = response.getAggregations().get("histo");
+        assertThat(histo, notNullValue());
+        assertThat(histo.getName(), equalTo("histo"));
+        List<? extends Bucket> buckets = histo.getBuckets();
+        assertThat(buckets.size(), equalTo(numValueBuckets + 3));
+
+        Histogram.Bucket bucket = buckets.get(0);
+        assertThat(bucket, notNullValue());
+        assertThat(((Number) bucket.getKey()).longValue(), equalTo((long) -1 * 2 * interval));
+        assertThat(bucket.getDocCount(), equalTo(0l));
+
+        bucket = buckets.get(1);
+        assertThat(bucket, notNullValue());
+        assertThat(((Number) bucket.getKey()).longValue(), equalTo((long) -1 * interval));
+        assertThat(bucket.getDocCount(), equalTo(0l));
+
+        for (int i = 2; i < numValueBuckets + 2; ++i) {
+            bucket = buckets.get(i);
+            assertThat(bucket, notNullValue());
+            assertThat(((Number) bucket.getKey()).longValue(), equalTo((long) (i - 2) * interval));
+            assertThat(bucket.getDocCount(), equalTo(valueCounts[i - 2]));
+        }
+    }
+
     public void testEmptyAggregation() throws Exception {
         SearchResponse searchResponse = client().prepareSearch("empty_bucket_idx")
                 .setQuery(matchAllQuery())