null checks in streams

[Jon Schewe]

I've got the code below 

private static Optional<String> findRangeShortDescriptionWithTitle(final String title,

final Goal goal) {

...

}

...

return scoreCategory.getAllGoals().stream()//

.filter(Goal.class::isInstance)//

.map(Goal.class::cast)//

.map(g -> findRangeShortDescriptionWithTitle(title, g))//

giving the following error

/home/jpschewe/projects/fll-sw/working-dir/src/main/java/fll/documents/writers/SubjectivePdfWriter.java:853: error: [argument] incompatible argument for parameter goal of SubjectivePdfWriter.findRangeShortDescriptionWithTitle.

.map(g -> findRangeShortDescriptionWithTitle(title, g))//

^

found : @Initialized @PolyNull Goal

required: @Initialized @NonNull Goal

I expect that checker wants the goal parameter to finRangeSHortDescriptionWithTitle to have @PolyNull on it. However before that is called in the stream the "isInstance" method is called and that will filter out nulls.

[Michael Ernst]

Jon-

Is Goal.isInstance annotated as returning a non-null value?

Is Goal.cast annotated as returning a polynull or a non-null value?

The argument "g in findRangeShortDescriptionWithTitle(title, g)" is non-null" depends on one or both of those facts.

(More generally, the more you can tell us about your code, the more helpful we can be.)

-Mike

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[Jon Schewe]

Goal.class.isInstance is built into the JDK, so it returns whatever checker ships with it returning.

The same goes for Goal.class.cast.

[Jon Schewe]

The method isInstance in java.lang.Class will return false for null. Therefore it's not possible for there to be a null in the stream pipeline after the call to isInstance. So how is the checker framework confused here? Does it not know that java.lang.Class.isInstance cannot return true for null? Or does the checker framework not track null checks through a stream pipeline?

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