Fix NPE bug in AggregateIterable

JAVA-2019

Author: rozza

driver/src/main/com/mongodb/AggregateIterableImpl.java

@@ -17,6 +17,7 @@
 package com.mongodb;
 
 import com.mongodb.client.AggregateIterable;
+import com.mongodb.client.FindIterable;
 import com.mongodb.client.MongoCursor;
 import com.mongodb.client.MongoIterable;
 import com.mongodb.client.model.FindOptions;
@@ -122,11 +123,15 @@ private MongoIterable<TResult> execute() {
                     .maxTime(maxTimeMS, MILLISECONDS)
                     .allowDiskUse(allowDiskUse);
             executor.execute(operation);
-            return new FindIterableImpl<TDocument, TResult>(new MongoNamespace(namespace.getDatabaseName(),
+            FindIterable<TResult> findOperation = new FindIterableImpl<TDocument, TResult>(new MongoNamespace(namespace.getDatabaseName(),
                                                                                outCollection.asString().getValue()),
                                                             documentClass, resultClass, codecRegistry, readPreference, executor,
                                                             new BsonDocument(),
-                    new FindOptions()).batchSize(batchSize);
+                    new FindOptions());
+            if (batchSize != null) {
+                findOperation.batchSize(batchSize);
+            }
+            return findOperation;
         } else {
             return new OperationIterable<TResult>(new AggregateOperation<TResult>(namespace, aggregateList, codecRegistry.get(resultClass))
                     .maxTime(maxTimeMS, MILLISECONDS)

driver/src/test/functional/com/mongodb/client/MongoCollectionTest.java

@@ -29,14 +29,17 @@
 import org.junit.Test;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
+import static com.mongodb.ClusterFixture.serverVersionAtLeast;
 import static java.util.Arrays.asList;
 import static org.bson.codecs.configuration.CodecRegistries.fromProviders;
 import static org.hamcrest.CoreMatchers.is;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertThat;
+import static org.junit.Assume.assumeTrue;
 
 public class MongoCollectionTest extends DatabaseTestCase {
 
@@ -137,6 +140,26 @@ public void testMapReduceWithGenerics() {
         assertEquals(new Name("Sam", 1), result.get(1));
     }
 
+    @Test
+    public void testAggregationToACollection() {
+        assumeTrue(serverVersionAtLeast(asList(2, 6, 0)));
+
+        // given
+        List<Document> documents = asList(new Document("_id", 1), new Document("_id", 2));
+
+        getCollectionHelper().insertDocuments(new DocumentCodec(), documents);
+
+        MongoCollection<Document> collection = database
+                .getCollection(getCollectionName());
+
+        // when
+        List<Document> result = collection.aggregate(Collections.singletonList(new Document("$out", "outCollection")))
+                .into(new ArrayList<Document>());
+
+        // then
+        assertEquals(documents, result);
+    }
+
     // This is really a test that the default registry created in MongoClient and passed down to MongoCollection has been constructed
     // properly to handle DBRef encoding and decoding
     @Test