![]() So we might name a field addressLine3OrNull, or a method previousAddressOrNull. Over the years, your authors and their colleagues settled into a convention where Java references are assumed to be nonnull unless otherwise flagged. We can deduce that methods that return an item from a collection must be able to return null, but can addressLine3 be null, or do we use an empty string when there is no information? Prior to Java 8, Java relied on convention, documentation, and intuition to distinguish between references that could or could not be null. This is another area where the grains of Java and Kotlin are different. If the library is reasonably popular, it is very likely that there is already a Kotlin alternative or companion library that will help you.Perhaps Kotlin’s most attractive feature for Java programmers is its representation of nullability in the type system. However, you are probably not the first to have this happen. Java libraries can sometimes cause problems in Kotlin. The individual commits show the original code with the failed test, the fix with the alternate matcher, and the final mock setup in Kotlin syntax. You can check the full code in my GitHub repository. In order for this code to compile, you need to add the following imports: import org. The method I was trying to stub was expecting a non-null String as an argument: interface MyDependency doReturn "Hello, World!" The cause was the any() argument matcher in my code to set up the method stub: val myDependencyMock = Mockito. When I ran the test, it failed with a NullPointerException: I recently ran into such a problem when trying to mock a dependency with Mockito. ![]() Unfortunately, it can sometimes cause problems when interacting with Java code or libraries. ![]() The null safety feature in Kotlin is great for preventing NullPointerExceptions that are thrown at runtime.
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