User information return null , while generate session

[tradenow]

I am generating session for the user but its return null

following code I am using

// Initialize Samart API using clientcode and password.
SmartConnect smartConnect = new SmartConnect();
////
//// // Provide your api key here
smartConnect.setApiKey("replace_your_key_here");
////
//// // Set session expiry callback.
smartConnect.setSessionExpiryHook(new SessionExpiryHook() {
@Override
public void sessionExpired() {
System.out.println("session expired");
}
});
////

    User user = smartConnect.generateSession("replce_client_code",
            "password");

// System.out.println(user.toString());

user return null , not fetch the user information ?