Via slashdot, the inventor of the null reference has second thoughts:

But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.

I am not a fan of null. It is a compiler level issue which has made its way into business and presentation logic; where it has no place. I would like a dollar for every time I have cleaned up a NullPointerException or littered my code with null checks.

Permalink, Inventor of Null References Changes His Mind

The Problem With Null

This is from an email that was sent to me by the Australian Democrats. They are doing the right thing and seeing who on their list is interested in being maintained on a subscriber list. The problem is the NULL value in the 'Dear NULL' line.

One of the things I hate about Null is that it is a compiler level issue that has somehow propogated to databases and nearly always ends up at a customer level because it litters presentation logic. There is no way that the end user of this email should even/ever be faced with the word Null.

In my opinion it is a fundamental flaw in software engineering that this problem still persists. No wonder the inventor of null wished he had not.

Kathryn: Hi Cam - firstly as the person who hit send on the email - sorry about that.

The problem was that on around 1200 records in the list of 36,000 someone had put NULL in to the name field. Had it been blank it would have said 'Friend'. I have fixed it all now... but if you'd like to email me from your email address so I can track you down in the system I'll put your name in so the next one says 'Dear Cam'. :D

cam: Hi Kathryn, I didnt mean to single out the Australian Democrats, it is a pet peeve of mine in software engineering how a low level issue like that is geared - by the structure of software tools and development methodologies - into presentation logic and a data state that is only meaningful to a software developer becomes one of perplexity for the end customer.

One system I worked on was endemic with NullPointerExceptions being blasted out to customers - stack trace and all. Usually front-end engineers have to clean up the mess that back end engineers make with their 'throw runtime exceptions' philosophy that gets around java's default state of checked exceptions. IMO software engineering has failed when these get to the customer.

Cast a Null in Java

I was working on unit test today to do with getSingleResult() from the EntityManager's query interface. I set the test up to check no results and then an outside exception. I had the query.getSingleResult() mocked to a null and got a surprising result.


context.checking(new Expectations() {{
    allowing(query).getSingleResult(); will (returnValue(null));
}});

It wasn't dropping into Exception as I expected. To my ignorance I was expecting a ClassCastException but in Java (and C#) null can cast to a type. I modified the test so that it did what I wanted and then went searching to see why you would want to cast a null.

This seemed to return the best answer. I still am not sure why it is a good idea to cast null, but in the case of method over-loading, it will ensure that the correct method is hit when passing in nulls as arguments.

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