Please try this. As my understanding it is not the select2 issue. I wrote selenium test below. And it is working for select and select2 both.
WebDriver driver=new FirefoxDriver();
driver.get("http://ivaynberg.github.io/select2/");
WebElement select=driver.findElement(By.id("e1"));
List<WebElement> options = select.findElements(By.tagName("option"));
for(WebElement option : options){
if(option.getText().equals("California")) {
option.click();
break;
}
}