invalid value (nil) at index 285 in table for 'concat'

error:

 [error] 6280#6280: *962711 lua entry thread aborted: runtime error: /usr/local/openresty/lualib/resty/shell.lua:136: invalid value (nil) at index 2 in table for 'concat'
stack traceback:
coroutine 0:
        [C]: in function 'concat'
        /usr/local/openresty/lualib/resty/shell.lua:139: in function 'run'

code:

        local shell = require "resty.shell"

        local stdin = nil
        local timeout = 10000  -- ms
        local max_size = 40960  -- byte

        local ok, stdout, stderr, reason, status =
            shell.run([[curl https://blockchain.info/q/getreceivedbyaddress/123]], stdin, timeout, max_size)

since that is a error output(ok == nil) now I just edit the stdout and stderr to nil in shell.lua;

...
136         local stdout = nil
137         release_tab(tab_pool_tag, stdout_tab)
138
139         local stderr = nil
140         release_tab(tab_pool_tag, stderr_tab)
...

Start with /usr/local/openresty/lualib/resty/shell.lua around lines 136-139 and reproduce the failure using shell.run with the curl command shown. Trace how error output is handled before table.concat; done means the command can return an error without triggering the nil-value concat runtime error.