When I only use top/bottom copper/mask layers in EasyEDA, the board outline is not detected by the JLCPCB order preview and gerber analysis.
Also, if the mask layer is empty, the mask is not shown on the order preview.
I have to add a hole/via/th-pad inside the board outline for it to work.
Example:




Chrome
85.0.4183.121
Windows
10
EasyEDA
6.4.7