Problem:
Since #23925, Version.build may be vim.NIL, which causes tostring() to fail:
E5108: Error executing lua E5114: Error while converting print argument #1: …/version.lua:129:
attempt to concatenate field 'build' (a userdata value)
stack traceback:
[C]: in function 'print'
[string ":lua"]:1: in main chunk
Solution:
Handle vim.NIL in Version:__tostring().
43e76cc346
