Error while running event shortwave::on_gui_closed (ID 84)
Given entity doesn't exist anymore.
stack traceback:
shortwave/control.lua:144: in function 'radio_tune'
shortwave/control.lua:297: in function <shortwave/control.lua:294>
stack traceback:
[C]: in function 'connect_neighbour'
shortwave/control.lua:144: in function 'radio_tune'
shortwave/control.lua:297: in function <shortwave/control.lua:294>

I think (haven't tested) this should fix it:

Replace lines 144-147 in control.lua:

    link.connect_neighbour({
            wire = defines.wire_type.red,
            target_entity = relay,
    })

with this:

    if link then
        link.connect_neighbour({
            wire = defines.wire_type.red,
            target_entity = relay,
        })
    end