Cannot read property 'hc' of nullcom

This looks like a GWT client side exception. If you don’t have your widgetset compilation style set to pretty (or something else i just forgot) it will show it like this.
To look at the “real” exception you can A ) like i said set the widgetset compilation style (for example in the project properties → Vaadin) to pretty and recompile the widgetset or B ) use one of the gwt dev modes.
More on these topics can be found on thiese forumes, the wiki or even the book of vaadin.

It is the same as

I wonder how I can fix this.

Looking at the first ticket you posted it says that the error only occurs when the server and client side aren’t correctly mapped so maybe you should check your @Connect(com.example.mycomponent.MyComponent.class) - mapping inside the Connector class.