Clicking 'x' on an empty buffer (made with :tabnew) creates error

[unphased]

E5108: Error executing lua /home/slu/.config/nvim/lua/heirline_conf/heirline.lua:865: Invalid buffer id: 8
stack traceback:
        [C]: in function 'nvim_win_set_buf'
        /home/slu/.config/nvim/lua/heirline_conf/heirline.lua:865: in function 'callback'
        ...hare/nvim/lazy/heirline.nvim/lua/heirline/statusline.lua:237: in function <...hare/nvim/lazy/heirline.nvim/lua/heirline/statusline.lua:236>

The buffer is removed from the tab bar (buffer bar) after the error, though.