ssdb.lua:51: no request found tcp()

[ghost]

nginx lua code:
local ssdb = require 'ssdb'
ssdbc = ssdb:new()
local ok, err = ssdbc:connect('127.0.0.1', 8888)
if not ok then
ngx.log(ngx.ERR, 'connect ssdb error')
end

exec: ./sbin/nginx -t
error：
nginx: the configuration file /usr/local/nginx-1.4.2//conf/nginx.conf syntax is ok
nginx: [error] init_by_lua_file error: /var/work/lua/ssdb.lua:51: no request found
stack traceback:
[C]: in function 'tcp'
/var/work/lua/ssdb.lua:51: in function 'new'
/var/work/lua/init.lua:171: in main chunk
nginx: configuration file /usr/local/nginx-1.4.2//conf/nginx.conf test failed