获取：“java.lang.NullPointerException”但我知道对象是在AsyncTask中实例化的

I am attempting to pass a string I got in an Asynchronous task class back in to my main activity, but when I pass the string result (which I know isn't null because logging the string right before passing it to the interface outputs what it should), I get a nullPointerException that says I can't pass a null object to the interface method.I am attempting to pass a string I got in an As