In 2019, we started a project called 0NPE with the goal of addressing this challenge within our apps and significantly improving null-safety of Java code through static analysis. These techniques are essential but have their own limitations in terms of time-to-signal and coverage. Since Java doesn’t provide tools to express and check nullness invariants, developers have to rely on testing and dynamic analysis to improve reliability of their code. On Android, NullPointerException (NPE) errors are the largest cause of app crashes on Google Play.

Null dereferencing is a common type of programming error in Java. This shows the value of static analysis in solving real-world problems at scale. Nullsafe has helped significantly reduce the overall number of NPE errors and improved developers’ productivity.

Interoperability with legacy code and gradual deployment model were key to Nullsafe’s wide adoption and allowed us to recover some null-safety properties in the context of an otherwise null-unsafe language in a multimillion-line codebase.We developed a new static analysis tool called Nullsafe that is used at Meta to detect NullPointerException (NPE) errors in Java code.

Null check in kotlin