As others have already pointed out, it's not data but rather likely data List that is null. In addition to that. catch-throw is an antipattern that almost always makes me want to throw up every time that I see it. Imagine that something goes wrong deep in something that do Other Stuff calls. All you get back is an Exception object, thrown at the throw in Add Data. No stack trace, no call information, no state, nothing at all to indicate the real source of the problem, unless you go in and switch your debugger to break on exception thrown rather than exception unhandled. If you are catching an exception and just re-throwing it in any way, particularly if the code in the try block is in any way nontrivial, do yourself (and your colleagues, present and future) a favor and throw out the entire try-catch block. Granted, throw; is better than the alternatives, but you are still giving yourself (or whoever else is trying to fix a bug in the code) completely unnecessary headaches. This is not to say that try-catch-throw is necessarily evil per se, as long as you do something relevant with the exception object that was thrown inside the catch block. Then there's the potential problems of catching Exception in the first place, but that's another matter, particularly since in this particular case you throw an exception. Another thing that strikes me as more than a little dangerous is that data could potentially change value during the execution of the function, since you are passing by reference. So the null check might pass but before the code gets to doing anything with the value, it's changed - perhaps to null. I'm not positive if this is a concern or not (it might not be but it seems worth watching out for.
A Null object is an object that encapsulates the absence of an object. It provides the do nothing behavior and returns the defaults. The Null object is used whenever object reference would have been null. The use of Null Object pattern simplifies the client code and makes it less error prone. Consider a simple sales application, which verifies the customer account and check whether customer does have the gold membership. Gold members get varied benefits like discount, free shipping etc. Below is the code snippet of the main method that gets the account details of the customers and retrieves their gold membership profile and applies all the benefits applicable to the gold members. string user Name = args[0]; string pin = args[1]; Order order = new Order for (int i = 2; i < args. Length; i+) order. Amount += Convert. To Decimal(args[i] var account = Account Controller. Get Account(user Name, pin if (account = null) Console. Write Line( Invalid Account else var g Profile = Gold Membership Controller. Get Profile(account if (g Profile!= null) order. Amount -= g Profile. Get Discount(order. Amount if (g Profile!= null) if (!g Profile. Is Shipping Free) order. Amount += order. Get Shipping Charges else order. Amount += order. Get Shipping Charges Console. Write Line(string. Format( Total Amount: 0, order. Amount If customer has the valid account then Account Controller. Get Account(user Name, pin) returns the Account object else it returns the null. Similarly if customer has gold membership then Gold Membership Controller. Get Profile(account) returns the Gold Membership object and in case user doesn't have gold membership, it returns the null. As you can see in the above code snippet, there are lots of repetitive conditional statements that check the null reference. Conditional statements are actually written to follow different paths based on the result of the condition. In the above gold.
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