How to get ajax status code from login field to use in testNG code?

I simulate test case when user forgets to input password and only inserts his phone number when login on website. Ajax has status attribute(true/false) for password field, but I don't know how to retrieve it and use it in java code.

I could not use Alert from selenium, because it does not detect alert itself

package com.example.tests;

import java.util.regex.Pattern;
import java.util.concurrent.TimeUnit;
import org.junit.*;
import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.*;
import org.openqa.selenium.*;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.support.ui.Select;

public class LoginTestNoPassword {
  private WebDriver driver;
  private String baseUrl;
  private boolean acceptNextAlert = true;
  private StringBuffer verificationErrors = new StringBuffer();

  @Before
  public void setUp() throws Exception {
    driver = new FirefoxDriver();
    baseUrl = "http://ift.tt/19BNkbL";
    driver.manage().timeouts().implicitlyWait(30, TimeUnit.SECONDS);
  }

  @Test
  public void testLoginTestNoPassword() throws Exception {
    driver.get(baseUrl + "/astana/login");
    driver.findElement(By.cssSelector("input.button.blue")).click();
  }

  @After
  public void tearDown() throws Exception {
    driver.quit();
    String verificationErrorString = verificationErrors.toString();
    if (!"".equals(verificationErrorString)) {
      fail(verificationErrorString);
    }
  }

  private boolean isAlertPresent() {
    try {
      driver.switchTo().alert();
      return true;
    } catch (NoAlertPresentException e) {
      return false;
    }
  }

}