Sending message from content script to background script breaks chrome extension

The problem was caused because my listener in background.js was not returning a response. So the function response of my chrome.extension.sendMessage was never being executed.

I changed my background.js to be:

chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
    if (request.type == "worktimer-notification")
      chrome.notifications.create('worktimer-notification', request.options, function() { });

    sendResponse();
});