Comment 41 for bug 1769383

@vanvugt: You're absolutely right, but the dockManager-instance is null because of an explicit exception in https://git.launchpad.net/ubuntu/+source/gnome-shell-extension-ubuntu-dock/tree/extension.js?h=ubuntu/bionic to disable ubuntu-dock if dash-to-dock is installed:

let to_enable = true;
let runningExtensions = ExtensionSystem.extensionOrder;
for (let i = 0; i < runningExtensions.length; i++) {
    if (runningExtensions[i] === "<email address hidden>") {
        to_enable = false;
    }
}

So i'm not able to fix this issue in the dash-to-dock repo. May we create a seperate bug report?