JAVA API: Fix source excludes setting if no includes were provided

Due to a bogus if-check in SearchSourceBuilder.fetchSource(String include, String exclude)
the excludes only got set when the includes were not null. Fixed this and added some
basic tests.

Closes #6632

src/main/java/org/elasticsearch/search/builder/SearchSourceBuilder.java

@@ -521,7 +521,7 @@ public SearchSourceBuilder fetchSource(boolean fetch) {
      * @param exclude An optional exclude (optionally wildcarded) pattern to filter the returned _source
      */
     public SearchSourceBuilder fetchSource(@Nullable String include, @Nullable String exclude) {
-        return fetchSource(include == null ? Strings.EMPTY_ARRAY : new String[]{include}, include == null ? Strings.EMPTY_ARRAY : new String[]{exclude});
+        return fetchSource(include == null ? Strings.EMPTY_ARRAY : new String[]{include}, exclude == null ? Strings.EMPTY_ARRAY : new String[]{exclude});
     }
 
     /**

src/test/java/org/elasticsearch/search/builder/SearchSourceBuilderTest.java

@@ -0,0 +1,86 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.elasticsearch.search.builder;
+
+import org.elasticsearch.common.xcontent.json.JsonXContent;
+import org.elasticsearch.test.ElasticsearchTestCase;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+
+import static org.hamcrest.Matchers.*;
+
+public class SearchSourceBuilderTest extends ElasticsearchTestCase {
+
+    SearchSourceBuilder builder = new SearchSourceBuilder();
+
+    @Test // issue #6632
+    public void testThatSearchSourceBuilderIncludesExcludesAreAppliedCorrectly() throws Exception {
+        builder.fetchSource("foo", null);
+        assertIncludes(builder, "foo");
+        assertExcludes(builder);
+
+        builder.fetchSource(null, "foo");
+        assertIncludes(builder);
+        assertExcludes(builder, "foo");
+
+        builder.fetchSource(null, new String[]{"foo"});
+        assertIncludes(builder);
+        assertExcludes(builder, "foo");
+
+        builder.fetchSource(new String[]{"foo"}, null);
+        assertIncludes(builder, "foo");
+        assertExcludes(builder);
+
+        builder.fetchSource("foo", "bar");
+        assertIncludes(builder, "foo");
+        assertExcludes(builder, "bar");
+
+        builder.fetchSource(new String[]{"foo"}, new String[]{"bar", "baz"});
+        assertIncludes(builder, "foo");
+        assertExcludes(builder, "bar", "baz");
+    }
+
+    private void assertIncludes(SearchSourceBuilder builder, String... elems) throws IOException {
+        assertFieldValues(builder, "includes", elems);
+    }
+
+    private void assertExcludes(SearchSourceBuilder builder, String... elems) throws IOException {
+        assertFieldValues(builder, "excludes", elems);
+    }
+
+    private void assertFieldValues(SearchSourceBuilder builder, String fieldName, String... elems) throws IOException {
+        Map<String, Object> map = getSourceMap(builder);
+
+        assertThat(map, hasKey(fieldName));
+        assertThat(map.get(fieldName), is(instanceOf(List.class)));
+        List<String> castedList = (List<String>) map.get(fieldName);
+        assertThat(castedList, hasSize(elems.length));
+        assertThat(castedList, hasItems(elems));
+    }
+
+    private Map<String, Object> getSourceMap(SearchSourceBuilder builder) throws IOException {
+        Map<String, Object> data = JsonXContent.jsonXContent.createParser(builder.toString()).mapAndClose();
+        assertThat(data, hasKey("_source"));
+        return (Map<String, Object>) data.get("_source");
+    }
+
+}