![]() ![]() In C# (until C# 7 ) there is the Nullable type which is only for value types but you can create your own or use a library.Ī straightforward approach is to replace a reference that can be null (by logic) with this type:Įach function that returns null will be converted to two functions. This solves the problem of NullPointerException raised in code areas away from the bug. When trying to access the value which doesn’t exist, it raises an exception. This type asks if a value exists and, if so, accesses the value. The option type is a different way to represent an optional value. I am not saying this is the best solution for every scenario - just options. I want to propose some technical patterns for eliminating null usage. In this book, Uncle Bob claims, we should not return nulls and should not pass null to a function. Martin, who is widely known as “Uncle Bob,” wrote one of the most famous books about clean code called (surprisingly) “Clean Code”. So what should we do? Listen to Uncle Bob Microsoft is adopting the same approach by introducing Nullable Reference Types in C#8. This allows catching the null assigned to non- null references, and making sure developers check for null before dereferencing nullable references, all at compile time. There are languages like Kotlin that aim to eliminate NullPointerException errors by differentiating between nullable references and non-nullable references. This poor design choice causes the problems I described before in “Hidden errors” and a lot of NullPointerException errors, of course. I believe most of the functions don’t return or accept null.īecause it is hard to know if a function returns null or not (unless documented), developers are either inserting null checks when not needed, or don’t check for nulls when needed - and yes, sometimes putting null checks when needed ?. This leads to a situation that we cannot know, by looking at a function signature, if null is a valid input or output of it. In C# and Java reference types can always point to null. It also makes the code branched and ugly ? Missing non-nullable reference types in C# and Java C an you see how this kind of null check can cause this situation ? When you arrive you discover you don’t have tickets! and there are no empty seats. You got a success message! The day of the show finally arrived, you leave work early, arrange a babysitter, and go to see the show. Imagine you buy a ticket to a show online. It also can cause a bug in some other functionality which assumed the other function did its job. Writing that kind of code means that some logic of a flow failed but the whole flow succeeded. Those kinds of null checks cause some code logic to not trigger, without the ability to know about it. “ I think this cannot be null but just to make sure, I don’t want it to blow up production”.“I know I should check for null but I don’t know what it means when the function returns null and I don’t know what to do with it,” or.I encounter null checks which seems like the developer was thinking: Real-life code can be much more complicated. But the NullPointerException is raised inside a function of class B. In the following code example, there is a bug, somewhere in class A, causing entity to be null. I am happy now but I will blow up eventually. It makes tracing the real problem harder. The code in which the NullPointerException is raised can be very far from where the bug is. What are the problems with using nulls? It will blow up. When we want to find an entity by criteria in a collection, we return null as a way to say the entity was not found. When we are at the top, we need a way to say so, usually it is by returning null. In hierarchical models, we usually can navigate up and down. When there is no data for an optional property, it returns null. Missing optional data for entitiesĪn entity’s property can be optional. I think it is an old school programming style, originating in the time when exceptions didn’t exist. ![]() This is one way of returning error codes. Returning null when the input is invalid. Here are some patterns I noticed in functions returning null: Error handling explicit assignment to null or returning null from a function.uninitialized reference-type class members.A bug can cause them never to be reassigned. “uninitialized” reference type variables - variables which are initialized with nulls and are assigned their real value afterward.We can get a reference to point to null in the following ways: In C# and Java, all reference types can point to null. The reason: developers use nulls too often. Why is this exception is so frequent? I argue (as does Uncle Bob ?) that it is n ot because developers forget to add null checks. Want to guess which one is in #1 place? NullPointerException. OverOps, an Israeli company which helps developers understand what happens in production, carried out research on what the top Java exceptions were in production. ![]()
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