In sb_lua_new_state() always push a value on stack before calling lua_setglobal().

sysbench/scripting/script_lua.c

@@ -411,10 +411,12 @@ lua_State *sb_lua_new_state(const char *scriptname, int thread_id)
         break;
       case SB_ARG_TYPE_FILE:
         /* FIXME: no need to export anything */
+        lua_pushnil(state);
         break;
       default:
         log_text(LOG_WARNING, "Global option '%s' will not be exported, because"
                  " the type is unknown", opt->name);
+        lua_pushnil(state);
         break;
     }