Uncaught (in promise) The message port closed before a response was received

// eslint-disable-next-line no-undef
chrome.runtime.onMessage.addListener((request, sender, sendResponse) => {
    if (request.dataNeeded === HANZI) {
        (async () => {                                       
            const hzl = await loadHanziListFile();                    
            sendResponse({data: hzl});
        })();
    
        // Need to return true if we are using async code in addListener.
        // Without this line..
        return true;
        // ..we will receive the error: 
        // Uncaught (in promise) The message port closed before a response was received
    }
});