@ApiStatus.Experimental
  public @NotNull Set<UnknownFeature> getUnknownFeaturesOfType(@NotNull @NonNls String featureType) {
    return myUnknownFeatures.stream()
      .filter(feature -> feature.getFeatureType().equals(featureType))
      .collect(Collectors.toUnmodifiableSet());
  }
@ApiStatus.Experimental
  public @NotNull Set<UnknownFeature> getUnknownFeaturesOfType(@NotNull @NonNls String featureType)