I'm trying to create a model with a optional, nullable string value. I've tried using both

  hint: types.optional(types.string, ""),

and

  hint: types.maybe(types.string),

Both results in error when I try to set a json object as to the object. Works if I manually loop through the json object and set the null content to empty string "".

Error while converting "jsoncontent" at path "content" value null is not assignable to type: string (Value is not a string).

I'm trying to create a model with a optional, nullable string value. I've tried using both

  hint: types.optional(types.string, ""),

and

  hint: types.maybe(types.string),

Both results in error when I try to set a json object as to the object. Works if I manually loop through the json object and set the null content to empty string "".

Error while converting "jsoncontent" at path "content" value null is not assignable to type: string (Value is not a string).

• javascript
• reactjs
• mobx
• mobx-state-tree

3 Answers 3

You can use types.maybeNull to have a type that can also be null.

hint: types.maybeNull(types.string)

You can use one of the following solutions to have a nullable string value in a Mobx-State-Tree:

types.maybeNull(types.string) // value can be null

or

types.optional(types.string, '') // should create empty string if value is not defined

I have created a helper function that allows you to simultaneously have optional and nullable types.

function nullOrUndefined<T extends IAnyType>(type: T) {
  return types.maybe(types.maybeNull(type));
}