code: public void setOptional(boolean optional) {
      if (field.getType().isPrimitive() || field.isAnnotationPresent(Version.class)
          || field.isAnnotationPresent(CreatedTimestamp.class)
          || field.isAnnotationPresent(UpdatedTimestamp.class)) {
        this.optional = false;
      } else {
        this.optional = optional;
      }
    }
docs: Sets whether or not the field represented by this metadata is optional.
  
  @param optional
  whether or not the field represented by this metadata is optional.