[3.0.0-rc1] Blank page when trying to create a Dashboard Widget

[halftrainedharry]

Bug report

Summary

When I try to create a new Dashboard Widget in the manager, no form is shown.

Step to reproduce

In the manager go to "Dashboards" -> tab "Widgets" -> click the "Create" button. (manager/?a=system/dashboards/widget/create)

Observed behavior

The panel on the right is blank. JS error in the console.

This line in the JS code throws an error, because Ext.getCmp('modx-extended-form') is undefined.

revolution/manager/assets/modext/widgets/system/modx.panel.dashboard.widget.js

Line 271 in d1c747d

Ext.getCmp('modx-extended-form').disable();

Possible solution

Check if Ext.getCmp('modx-extended-form') is defined before trying to call .disable() on it.

if (Ext.getCmp('modx-extended-form')){
    Ext.getCmp('modx-extended-form').disable();
}
//or maybe
Ext.getCmp('modx-extended-form')?.disable();

Expected behavior

The form to create a widget is shown.

Environment

MODX 3.0.0-rc1

[JoshuaLuckers]

Would it be possible for you to submit a PR with the proposed solution?

[Ibochkarev]

Fixed #15987