FP java:S2637 when collecting stream to list, using JSpecify nullability annotations

Rules and Languages Report False-positive / False-negative...
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In a Java program using JSpecify notations, SonarQube Cloud warns that a method marked @NonNull may return null, when it may not:

package com.example;

import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;
import java.util.List;
import java.util.Objects;
import java.util.stream.Stream;

public class SonarExample {
  @NonNull
  public List<String> getStrings() {
    // Sonar says: "This method's return value is marked "@NullMarked at class level" but null is returned."
    return Stream.of("one", "two", "three")
        .map(SonarExample::toUppercase)
        .filter(Objects::nonNull)
        .toList();
  }

  @Nullable
  private static String toUppercase(final String string) {
    if (string.equals("two")) {
      return null;
    }
    return string.toUpperCase();
  }
}

Same happens when using @NullMarked on the class instead of @NonNull on the getStrings method.

If @Nullable is removed on toUppercase, the warning goes away.