package ai.api.model;

/***********************************************************************************************************************
 *
 * API.AI Android SDK - client-side libraries for API.AI
 * =================================================
 *
 * Copyright (C) 2015 by Speaktoit, Inc. (https://www.speaktoit.com)
 * https://www.api.ai
 *
 ***********************************************************************************************************************
 *
 * Licensed 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.
 *
 ***********************************************************************************************************************/

import com.google.gson.annotations.SerializedName;

import java.io.Serializable;

public class Fulfillment implements Serializable {

    @SerializedName("speech")
    private String speech;

    public String getSpeech() {
        return speech;
    }

    public void setSpeech(final String speech) {
        this.speech = speech;
    }
}

package ai.api.model;

/***********************************************************************************************************************
 *
 * API.AI Android SDK - client-side libraries for API.AI
 * =================================================
 *
 * Copyright (C) 2015 by Speaktoit, Inc. (https://www.speaktoit.com)
 * https://www.api.ai
 *
 ***********************************************************************************************************************
 *
 * Licensed 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.
 *
 ***********************************************************************************************************************/

import com.google.gson.JsonElement;
import com.google.gson.annotations.SerializedName;

import java.io.Serializable;

public class Fulfillment implements Serializable {

    @SerializedName("speech")
    private String speech;

    @SerializedName("displayText")
    private String displayText;

    @SerializedName("data")
    private JsonElement data;

    @SerializedName("source")
    private String source;

    public String getSpeech() {
        return speech;
    }

    public void setSpeech(final String speech) {
        this.speech = speech;
    }

    public JsonElement getData() {
        return data;
    }

    public void setData(final JsonElement data) {
        this.data = data;
    }

    public String getDisplayText() {
        return displayText;
    }

    public void setDisplayText(final String displayText) {
        this.displayText = displayText;
    }

    public String getSource() {
        return source;
    }

    public void setSource(final String source) {
        this.source = source;
    }
}

Add new fields to Fulfillment class