Kong upgrade problem from 0.10.3 to 0.11.1

[apple4196]

Hello, I had some problem when I upgrade my Kong service. I followed the instroctions of the official website as below:

1.download kong-community-edition-0.11.1.el6.noarch.rpm and installed it.

2.run the new cassandra database (from cassandra 2.2.9 to cassandra 3.11.1)

3.run command:  kong migrations up -c /etc/kong/kong.conf

4.kong start

But when I was starting the kong , I get this error message:

Error: /usr/local/share/lua/5.1/kong/cmd/start.lua:51: nginx: [error] init_by_lua error: /usr/local/share/lua/5.1/pl/utils.lua:125: argument 1 expected a 'string', got a 'nil'

stack traceback:

        [C]: in function 'error'

        /usr/local/share/lua/5.1/pl/utils.lua:429: in function 'assert_arg'

        /usr/local/share/lua/5.1/pl/utils.lua:441: in function 'assert_string'

        /usr/local/share/lua/5.1/pl/utils.lua:125: in function 'read'

        /usr/local/share/lua/5.1/kong/serf.lua:26: in function 'new'

        /usr/local/share/lua/5.1/kong.lua:155: in function 'init'

        init_by_lua:3: in main chunk

  Run with --v (verbose) or --vv (debug) for more details

[dmnadm@wddpapigate1 ~]$ kong start -c /etc/kong/kong.conf

Error: /usr/local/share/lua/5.1/kong/cmd/start.lua:51: nginx: [error] init_by_lua error: /usr/local/share/lua/5.1/pl/utils.lua:125: argument 1 expected a 'string', got a 'nil'

stack traceback:

        [C]: in function 'error'

        /usr/local/share/lua/5.1/pl/utils.lua:429: in function 'assert_arg'

        /usr/local/share/lua/5.1/pl/utils.lua:441: in function 'assert_string'

        /usr/local/share/lua/5.1/pl/utils.lua:125: in function 'read'

        /usr/local/share/lua/5.1/kong/serf.lua:26: in function 'new'

        /usr/local/share/lua/5.1/kong.lua:155: in function 'init'

        init_by_lua:3: in main chunk

Did I miss anything? 

BTW, this is my first time to ask question on a community, if there is any opnion(like the problem description...), just tell me , thx.