Extension showing issues between VSCode treeView viewsWelcome and treeView message.
In the doc it says that treeView's viewsWelcome must be shown when the treeView has no element and no message. Apparently setting the message to an empty string '' or to undefined, as it is allowed by the API typing, is not enough to make VSCode consider showing the viewsWelcome.
This extension exposes an empty tree with a viewsWelcome and a message set to undefined, you can launch the extension to see that the treeView.message does not appear