code: public static <S extends Model> Object getAndRemovePrimaryKey(S model) {
          String fieldName = getPKField(model.getClass());
          Object value     = invokeMethod(model, getGetterName(fieldName), EMPTY_ARG);
          if (null != value) {
              invokeMethod(model, getSetterName(fieldName), NULL_ARG);
          }
          return value;
      }
docs: Return the primary key of the model and set it to null
  
  @param model db model
  @param <S>   model generic type
  @return primary key value