尝试索引全局变量'e_con'(一个数字值)

lua: els_bgapi.lua:20: 尝试索引全局变量'e_con'(一个数字值)
stack traceback:
        els_bgapi.lua:20: in main chunk
        [C]: in ?

请帮我，我是 Lua 和 FreeSWITCH 的新手。运行下面的代码时出现了上面的错误

sock:bgapi("originate","{sip_cid_type=pid,origination_uuid=uuid,origination_caller_id_number=65181,originate_timeout=10}sofia/external/sip:81245@10.20.16.135 5000")

e_con= sock:events("plain","all");
if (e_con) then
  print(e_con:getHeader());
else
  print("not e_con")
end