I check the thread, it's the same procedure that I made.
When you create an item under NewsBackendList > SideBar > Sections with similar settings as tag or category, you break the list of News in Backend it doesn't load (blank page because of JS error).
If under your custom section you try to create a DynamicCommandWidgetElement, you obtains this error :
threw the following exception:
'Object reference not set to an instance of an object.'
And I tried a workaround with manually edition of configuration files, but it activate another exception.