The following code produces a warning on the parameter "a":

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Stream.of(1, 2).filter(a -> true);
Stream.of(1, 2).filter((Integer a) -> true);
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The following code, however, doesn't:

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Stream.of(1, 2).filter(new Predicate<Integer>() {
    @Override
    public boolean test(Integer a) {
        return true;
    }
});
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The warning is not really necessary. It would be better not to report it (or at least make reporting it an option, and not report it by default)