Reports transform operations that may return null inside a Reactive Stream chain.

Reactive Streams don't support null values, which causes such code to fail.

Example:

repository.findWithTailableCursorBy()
    .map(e -> (Person)null)
    .doOnNext(System.out::println)

It is better not to use nullable values inside a Reactive Stream chain code, but if it is necessary, use special operations, like Reactor's mapNotNull.

There is a quick-fix for replacing map with mapNotNull. It omits exceptions, because mapNotNull allows null values.

Before quick-fix:

repository.findWithTailableCursorBy()
    .map(e -> (Person)null)
    .doOnNext(System.out::println)

After the quick-fix is applied:

repository.findWithTailableCursorBy()
    .mapNotNull(e -> (Person)null)
    .doOnNext(System.out::println)

New in 2019.3