Fix ignoring missing values in min/max aggregations (elastic#48970)

Fixes the issue when the missing values can be ignored in min/max
due to BKD optimization.

Fixes elastic#48905

Author: imotov

server/src/main/java/org/elasticsearch/search/aggregations/metrics/MinAggregator.java

@@ -181,7 +181,7 @@ static Function<byte[], Number> getPointReaderOrNull(SearchContext context, Aggr
         if (parent != null) {
             return null;
         }
-        if (config.fieldContext() != null && config.script() == null) {
+        if (config.fieldContext() != null && config.script() == null && config.missing() == null) {
             MappedFieldType fieldType = config.fieldContext().fieldType();
             if (fieldType == null || fieldType.indexOptions() == IndexOptions.NONE) {
                 return null;

server/src/test/java/org/elasticsearch/search/aggregations/metrics/MaxAggregatorTests.java

@@ -87,6 +87,7 @@
 import java.util.function.Function;
 import java.util.function.Supplier;
 
+import static java.util.Collections.emptyList;
 import static java.util.Collections.singleton;
 import static org.elasticsearch.index.query.QueryBuilders.termQuery;
 import static org.hamcrest.Matchers.equalTo;
@@ -232,6 +233,22 @@ public void testUnmappedWithMissingField() throws IOException {
         }, null);
     }
 
+    public void testMissingFieldOptimization() throws IOException {
+        MappedFieldType fieldType = new NumberFieldMapper.NumberFieldType(NumberFieldMapper.NumberType.INTEGER);
+        fieldType.setName("number");
+
+        MaxAggregationBuilder aggregationBuilder = new MaxAggregationBuilder("_name").field("number").missing(19L);
+
+        testCase(aggregationBuilder, new MatchAllDocsQuery(), iw -> {
+            iw.addDocument(Arrays.asList(new IntPoint("number", 7), new SortedNumericDocValuesField("number", 7)));
+            iw.addDocument(Arrays.asList(new IntPoint("number", 1), new SortedNumericDocValuesField("number", 1)));
+            iw.addDocument(emptyList());
+        }, max -> {
+            assertEquals(max.getValue(), 19.0, 0);
+            assertTrue(AggregationInspectionHelper.hasValue(max));
+        }, fieldType);
+    }
+
     public void testScript() throws IOException {
         MappedFieldType fieldType = new NumberFieldMapper.NumberFieldType(NumberFieldMapper.NumberType.INTEGER);
         fieldType.setName("number");