Okay, your closeModelButton should look something like this.
public void clickCloseModalButton()
{
WebDriverWait wait = new WebDriverWait(driver, 25); // choose your time to wait for model dialog here
wait.until(ExpectedConditions.visibilityOfElementLocated(closeModalButton));
if(driver.findElement(closeModalButton).isVisible()){//This will make it optional.
driver.findElement(closeModalButton).click();
}
}