gson serialization yields null

LoginInfo.java

package test;

import java.util.List;

public class LoginInfo {
	public class DeviceInfo {
		public String deviceId;
		public String deviceType;
		public String deviceOs;
		public int deviceVersion;
		public boolean deviceScanAlways;
	}

	public class SdkIdentity {
		public String sdkKey;
		public String userId;
	}

	public class Data {
		public DeviceInfo deviceInfo;
		public List<SdkIdentity> sdk_identities;
	}
	
	public Data data;

}

output

null

Test.java

package test;

import java.util.ArrayList;

import com.google.gson.Gson;

public class Test {

	public static void main(String[] args) {
		LoginInfo loginInfo = new LoginInfo() {
			{
				data = new Data() {
					{
						deviceInfo = new DeviceInfo() {
							{
								deviceId = "dfs";
								deviceOs = "";
								deviceScanAlways = false;
								deviceVersion = 5;
								deviceType = "type";
								
							}
						};
						sdk_identities = new ArrayList<SdkIdentity>() {
							{
								add(new SdkIdentity() {
									{
										sdkKey = "xxx";
										userId = "none";
									}
								});
							}
						};
						
					}
				};
			}
		};
		
		Gson gson = new Gson();
		System.out.println(gson.toJson(loginInfo));
	}

}

public static void main(String[] args) {

    LoginInfo loginInfo = new LoginInfo();      

    Data data = loginInfo.new Data();
    data.sdk_identities = new ArrayList<LoginInfo.SdkIdentity>();

    loginInfo.data = data;

    Gson gson = new Gson();
    System.out.println(gson.toJson(loginInfo));
}