I’ve been looking at Function.java from Microsoftjdk-17.0.11.9-hotspotlibsrc.zip!java.basejavautilfunctionFunction.java

It appears like this in IntelliJ IDEA 2024 :

I couldn’t help but notice that there’s an automated (inferred) @NotNull added by IntelliJ in front of Function<...> in the method prototype.

Where does the @NotNull come from? In other words : What does this class have that my own classes don’t have? (None of my classes make IntelliJ add @NotNull spontaneously even when the context makes it clear).

Note: I looked at annotation @FunctionalInterface ‘s inner workings but could not find a direct link between how it works and this @NotNull. Maybe it’s there, I just don’t see it.