doing so will cause adding layer or painting impossible,you have to close the current project,but what is on the canvas can still be exported to images
I can confirm the issue. The problem is, there are no layers anymore. The conversion code should check whether there is more than one layer before converting.
(I can confirm on Ubuntu 14.04 - Krita 4.0.0-beta1.1.appimage)
"Undo (CTRL+Z)" should help to restore the "Layers" docker.
I can also confirm this issue with Krita 4.1.1, and as mvowada said "Undo (Ctrl+Z)" does restore everything correctly.
Git commit 0355e1abe8815db61046d050936ca8915c31ee52 by Agata Cacko. Committed on 19/06/2019 at 13:34. Pushed by tymond into branch 'master'. Fix converting lonely layer to selection mask When you have only one layer in the image, you can still convert it into a mask: filter mask, selection mask or transparency mask. In case of filter and transparency masks, a new layer was created. Before this commit, converting to selection mask caused Krita to enter a state where there was no layers in Layers docker. This commit makes sure that converting a lonely layer into a selection mask will trigger creating new layer as well. Note that the added check is important because the root layer allows selection mask to be its child because of Global Selection Mask (that was also the reason why only the selection mask worked the way it worked) - that's why Krita needs to check the parent node explicitely for being a root. M +2 -1 libs/ui/kis_mask_manager.cc https://invent.kde.org/kde/krita/commit/0355e1abe8815db61046d050936ca8915c31ee52