** Marks a field as a property of a JSON document.@Jsfacet class JsonProperty {** Name of the JSON object property this field maps to. ** ** Defaults to the field name.const Str? propertyName** The implementation 'Type' to use when instantiating this object. ** Use when this field references a mixin or a superclass. ** ** Defaults to the field type.const Type? implType** Dictates whether or not 'null' values are persisted in JSON objects.** ** If 'null' then the decision is deferred to the 'ObjConverter' implementation, which is 'false' by default.** ** Note that the 'null' check is performed on the JSON value *after* any conversion. const Bool? storeNullValues** Use to name a custom JSON '<->' Fantom Converter. The type should extend 'JsonConverter'.** ** The converter should have a no-args ctor or, if using IoC, a ctor suitable for autobuild. const Type? converterType}