Set<Feature<?>> morePresentFeatures = moreRequirements.getPresentFeatures();
    Set<Feature<?>> moreAbsentFeatures = moreRequirements.getAbsentFeatures();
    checkConflict("absent", absentFeatures, "present", morePresentFeatures, source);
    checkConflict("present", presentFeatures, "absent", moreAbsentFeatures, source);
    presentFeatures.addAll(morePresentFeatures);
    absentFeatures.addAll(moreAbsentFeatures);