Click the button with the HtmlUnit - Java

Question

I am unable to click a button to HtmlUnit , already tried by the name and ID , it does not have a Value, already I put waiting and still nothing .

HtmlButton button = (HtmlButton) page2.getElementById("imbInserir");

  try {
  button.click();
  }catch(Exception e) {
      System.out.println("I could not push the button");
      e.printStackTrace();
      return;
  }  
   }
}

Html Page Button:

<input type="image" name="ctl00$ContentPlaceHolderConteudoPagina$dtvFiltragem$imbInserir" id="imbInserir" title="Inserir Apontamento" src="../Imagens/inserir.png">

Console:

java.lang.NullPointerException at htmlunit.Acesso.main(Acesso.java:74)