If I copy an existing style and assign it to the same layer it belong to, the GetCapabilities fails with a NullPointerException.
Start the platform independent binary package
Notice the Layer is listed and the styles list is available
Login to the admin panel
Go to Styles and select "Add new style"
Give it a name
From "Copy from existing style" select "population" and hit "copy"
The "Publishing" tab should appear
Open the "Publishing" tab
In the "topp" "states" line, tick "Default" and "Associated" checkboxes
Notice no styles are available
Check the logs, see the NullPointerException
The log is:
Tested on CentOS 7 and Windows 10