Added Builder for Derivatives Reducer

src/main/java/org/elasticsearch/search/aggregations/reducers/derivative/DerivativeBuilder.java

@@ -0,0 +1,48 @@
+/*
+ * 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.aggregations.reducers.derivative;
+
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.search.aggregations.reducers.ReducerBuilder;
+
+import java.io.IOException;
+
+public class DerivativeBuilder extends ReducerBuilder<DerivativeBuilder> {
+
+    private String format;
+
+    public DerivativeBuilder(String name) {
+        super(name, DerivativeReducer.TYPE.name());
+    }
+
+    public DerivativeBuilder format(String format) {
+        this.format = format;
+        return this;
+    }
+
+    @Override
+    protected XContentBuilder internalXContent(XContentBuilder builder, Params params) throws IOException {
+        if (format != null) {
+            builder.field(DerivativeParser.FORMAT.getPreferredName(), format);
+        }
+        return builder;
+    }
+
+}

src/main/java/org/elasticsearch/search/aggregations/reducers/derivative/DerivativeParser.java

@@ -33,8 +33,6 @@ import java.util.ArrayList;
 import java.util.List;
 
 public class DerivativeParser implements Reducer.Parser {
-
-    public static final ParseField BUCKETS_PATH = new ParseField("bucketsPath");
     public static final ParseField FORMAT = new ParseField("format");
 
     @Override