Note that, the wizard generates public setUserNamePassword method:
=========================
public void setUsernamePassword(String username, String password) {
        client.register(new org.glassfish.jersey.client.filter.HttpBasicAuthFilter(username, password));
    }
=========================
 which is rather late to call after webTarget is initialized in constructor.

The correct code should be:
=========================
void setUsernamePassword(String username, String password) {
        webTarget.register(new org.glassfish.jersey.client.filter.HttpBasicAuthFilter(username, password));
    }
=========================
May be, generate also another constructor with username, password parameters.