When using a method reference with lambda, a @Nonnull warning will be prompted #4451

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1. t3cssd

   added

   bug

   on Jun 30, 2026
2. wenytang-ms commented on Jul 3, 2026

   

   wenytang-ms

   on Jul 3, 2026

   Last edited by wenytang-ms

   Contributor

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   Hey, thanks for the report

   Quick heads-up first: this isn't really about method references. It's the annotation-based null analysis kicking in. If you swap Class::getXxxx for a plain lambda like x -> x.getXxxx(), you get the exact same warning — the squiggle just happens to land on the Comparator.comparing(...) call, which visually overlaps the method reference.

   What's going on under the hood: the null analysis is done by Eclipse JDT (ecj), vscode-java just turns it on. The JDK standard library (Comparator, Function, and your own getter) doesn't carry any nullness annotations, so once your code sits in a nonnull-by-default context, the analyzer treats those as "null-unknown" and warns that they might not be @NonNull. It simply has no way to know that e.g. Comparator.comparing never returns null, because nothing tells it so.

   That's also why it only shows up when (a) null analysis is enabled and (b) there's a @NonNull target around the call. Drop the nonnull-by-default and it goes quiet.

   A couple of options if it's getting in your way:

   • If you don't really need null analysis, set java.compile.nullAnalysis.mode to disabled.
   • If you do want to keep it, the real answer is external annotations for the JDK so the analyzer knows those methods are non-null — that's the broader topic already tracked in Recognize contractual non-nullness of standard library functions #2731.

   Linking this to #2731 since it's the same underlying thing (recognizing the non-nullness of standard-library methods).