Null Check Analysis

Osman, Haidar (July 2015). Null Check Analysis. In: Extended Abstracts of the Eighth Seminar on Advanced Techniques and Tools for Software Evolution (SATToSE 2015). Mons, Belgium. 06.-08.07.2015.

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Null dereferencing is one of the most frequent bugs in Java systems causing programs to crash due to the uncaught NullPointerException. Developers often fix this bug by introducing a guard (i.e., null check) on the potentially-null objects before using them. In this paper we investigate the null checks in 717 open-source Java systems to understand when and why developers introduce null checks. We find that 35 of the if-statements are null checks. A deeper investigation shows that 71 of the checked-for-null objects are returned from method calls. This indicates that null checks have a serious impact on performance and that developers introduce null checks when they use methods that return null.

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