deserialize JSON to an ArrayList with Flexjson (Java Android)

Question

I want to deserialize this json data into an ArrayList

{"users":[{"username":"jon@jafprod.com","pw":"123456","data":""},{"username":"fred@jones.com","pw":"abcde","data":""}]}

this is the class

public class UserClass
{
    public String email;
    public String pw;
    public JSONObject data;
}

My attempts such as:

UserClass users = new JSONDeserializer<UserClass>().use("users", UserClass.class)
                    .deserialize( resultStr, Array.class );

but always result in a java.lang.NoClassDefFoundError: Failed resolution of: Lflexjson/JSONDeserializer;