callbacks property Null safety

Map<String, APICallback>? callbacks
read / write

A map of possible out-of band callbacks related to the parent operation.

The key is a unique identifier for the APICallback. Each value in the map is a APICallback that describes a request that may be initiated by the API provider and the expected responses. The key value used to identify the callback object is an expression, evaluated at runtime, that identifies a URL to use for the callback operation.

Implementation

Map<String, APICallback>? callbacks;