从模型中删除动态禁用的值（通过`expressionProperties`）字段？

When an angular-formly (I am using v6.4.x w/ AngularJS 1.2.x) field's expression property causes the field to dynamically toggle between enabled and disabled, a switch to disabled does not remove any previously entered value for that field from the model. For example: (I am using v6.4.x w/ An