title: sendKeys() not working with HtmlUnitDriver
body: <p>I have this code</p>
  
  <pre><code>public static void switchUser(HtmlUnitDriver driver, String uid) {
  
      WebElement username = driver.findElement(By.id("principal_uid"));        
      username.sendKeys(uid);
  </code></pre>
  
  <p>This worked just fine when I used it FirefoxDriver, but since I change it to HtmlUnitDriver it stopped. My problem has 2 aspects:</p>
  
  <ol>
  <li><code>SendingKeys()</code> does not fill the username field at all. Calling <code>username.getText()</code> returns blank.</li>
  <li>I need the sendKeys to be finished with a press of Enter, which seems to be a hard one to HtmlUnitDriver. Calling <code>username.sendKeys(Keys.RETURN);</code> gives <code>NullPointerException</code>.</li>
  </ol>
  
  <p>Tell me a way to fix this.Could it be because username field triggers onChange javascript?</p>