docs: @Requires("modifier != null")
    @Ensures("!getModifiers().contains(modifier)")
    public void removeModifier(ElementModifier modifier) {
      modifiers.remove(modifier);
      switch (modifier) {
        case PRIVATE:
        case PACKAGE_PRIVATE:
        case PROTECTED:
        case PUBLIC:
          modifiers.add(ElementModifier.PACKAGE_PRIVATE);
      }
    }