How can I avoid the null object reference error - apache-flex

Question

I have function init, which runs on the creationComplete of the application. The init calls get_login_share_object function, in which objects are created, which are null.
Now my problem is that, I get a null object reference error on the Alert in "init()". How can I avoid that. Is it possible that I can have a check to see, if the objects are null the program should just skip reading the objects.
private function init():void
{
var stored_credentials:Object = get_login_share_object();
Alert.show(stored_credentials.check_remember +" "+ stored_credentials.alias +" "+ stored_credentials.password );
}
private function get_login_share_object():Object
{
//create or retrieve the current shared object
var so:SharedObject = SharedObject.getLocal("loginData","/");
var dataToLoad:ByteArray = so.data.ws_creds;
if(!dataToLoad)
return null;
//read in our key
var aes_key:String = ServerConfig.aes_key;
var key:ByteArray = new ByteArray();
key = Base64.decodeToByteArray(aes_key);
//read in our encryptedText
var encryptedBytes:ByteArray = new ByteArray();
dataToLoad.readBytes(encryptedBytes);
//decrypt using 256b AES encryption
var aes:ICipher = Crypto.getCipher("simple-aes128-ctr", key, Crypto.getPad("pkcs5"));
aes.decrypt(encryptedBytes);
encryptedBytes.position = 0;
var obj:Object = new Object();
obj.alias = encryptedBytes.readUTF();
obj.password = encryptedBytes.readUTF();
obj.check_remember = encryptedBytes.readUTF();
return obj;
}

Answer 1

You could check for the null like this:
var stored_credentials:Object = get_login_share_object();
if (stored_credentials)
Alert.show(stored_credentials.check_remember +" "+ stored_credentials.alias +" "+ stored_credentials.password );
else
trace('No Shared Object');

Answer 2

You should find out why those values are null and fix that first. Generally speaking, if you are expecting a value, it should not be null.
If it really is expected that some of those values are null then yes, you can check them first in two ways:
if(value != null) value.doSomething();
or
try{
Alert.show(stored_credentials.check_remember +" "+ stored_credentials.alias +" "+ stored_credentials.password );
}
catch(e:Error){
// do something else here if the statement under the try failed.
// most likely log the error message and see what it is
}

Answer 3

Your problem is here:
var dataToLoad:ByteArray = so.data.ws_creds;
if(!dataToLoad)
return null;
If there isn't any data to load, you're returning a null. So when you try and access the returned object's properties later, you'll get the null object reference error because you're referencing a null object. :)
There are a couple of easy solutions to this. You can check if the return value is null before you try to reference any properties like so:
if (stored_credentials != null) {
Alert.show(stored_credentials.check_remember +" "+ stored_credentials.alias +" "+ stored_credentials.password );
}
Or you can stop returning a null from your get_login_share_object function. What you return instead is totally up to you, just make sure it returns an object with all the properties you're referencing.