calling set_var with multiple parameters

[ash...@tibco.com]

I'm trying to call an nginx directive that sets a single variable but accepts multiple parameters.
Ex https://github.com/openresty/set-misc-nginx-module#set_hmac_sha1

I get "expecting one argument" from https://github.com/openresty/lua-nginx-module/blob/master/src/ngx_http_lua_ndk.c#L76

Am I calling the wrong method or does that code need to be modified?