Correctly handle null values in time column results (#10642)

* handle null case

* test this case

* test sql resource

* fix style

sql/src/main/java/org/apache/druid/sql/http/SqlResource.java

@@ -134,7 +134,9 @@ public class SqlResource
                       for (int i = 0; i < fieldList.size(); i++) {
                         final Object value;
 
-                        if (timeColumns[i]) {
+                        if (row[i] == null) {
+                          value = null;
+                        } else if (timeColumns[i]) {
                           value = ISODateTimeFormat.dateTime().print(
                               Calcites.calciteTimestampToJoda((long) row[i], timeZone)
                           );

sql/src/test/java/org/apache/druid/sql/http/SqlResourceTest.java

@@ -325,6 +325,31 @@ public class SqlResourceTest extends CalciteTestBase
     );
   }
 
+  @Test
+  public void testTimestampsInResponseWithNulls() throws Exception
+  {
+    final List<Map<String, Object>> rows = doPost(
+        new SqlQuery(
+            "SELECT MAX(__time) as t1, MAX(__time) FILTER(WHERE dim1 = 'non_existing') as t2 FROM druid.foo",
+            ResultFormat.OBJECT,
+            false,
+            null,
+            null
+        )
+    ).rhs;
+
+    Assert.assertEquals(
+        NullHandling.replaceWithDefault() ?
+        ImmutableList.of(
+            ImmutableMap.of("t1", "2001-01-03T00:00:00.000Z", "t2", "-292275055-05-16T16:47:04.192Z") // t2 represents Long.MIN converted to a timestamp
+        ) :
+        ImmutableList.of(
+            Maps.transformValues(ImmutableMap.of("t1", "2001-01-03T00:00:00.000Z", "t2", ""), (val) -> "".equals(val) ? null : val)
+        ),
+        rows
+    );
+  }
+
   @Test
   public void testFieldAliasingSelect() throws Exception
   {