Null propagation doesn't work between Java Stream operations

A common pattern in some codebases is to filter streams by the keys of a map:

  private Stream<String> filterBasedOnMapKeys(Map<String, String> map, Stream<String> stream) {
    return stream
            .filter(map::containsKey)
            .map(value -> someMethod(map.get(value)));
  }

This fails the null check, claiming that the method someMethod is being passed a nullable value when not null is required. However, as the stream has already been filtered, the .get(...) call is safe.

Start with the Java stream reproducer in the issue and locate the NullAway analysis entry points and tests covering stream operations and map lookups. Determine how nullness is propagated across the filter and map chain; done means this pattern no longer reports a nullable argument while unsafe lookups remain diagnosed.