Feature request: @IsNullable

[andybarron]

A version of @IsOptional that would allow null but not undefined would be a great add for a lot of use cases. Additionally, a version that allowed undefined but not null would come in handy for certain operations as well - I would think this is what @IsOptional should do, but the docs state that it allows null AND undefined, which I don't think is particularly intuitive.

[Kiliandeca]

This seems to be related to #491

[rubiin]

why not use a custom validator?

[NickKelly1]

Right now you can accomplish this using a custom decorator.

Reposting my solution from here:

You can create "optionally null" and "optionally undefined" decorators by decorating the @ValidateIf decorator

/**
 * Skips validation if the target is null
 */
function IsNullable(options?: ValidationOptions): PropertyDecorator {
  return function IsNullableDecorator(prototype: Object, propertyKey: string | symbol) {
    ValidateIf((obj) => (obj)[propertyKey] !== null, options)(prototype, propertyKey);
  };
}

/**
 * Skips validation if the target is undefined
 */
function IsUndefinable(options?: ValidationOptions): PropertyDecorator {
  return function IsUndefinedDecorator(prototype: Object, propertyKey: string | symbol) {
    ValidateIf((obj) => (obj)[propertyKey] !== undefined, options)(prototype, propertyKey);
  };
}

[ynishimura]

I'm happy that @IsNullable is provided as a feature rather than using a custom validator.