How to use the mobx-utils.lazyObservable function in mobx-utils

this.getCapabilities = mobxUtils.createTransformer(terria => {
            const url = this.getCapabilitiesUrl;
            return mobxUtils.lazyObservable(sink => {
                loadXML(url).then(sink);
            }, undefined).current();
        });

constructor() {
        this.operation = lazyObservable(async sink => {
            sink(null);
            const result = await this.performOperation();
            sink(result);
        });
    }