Runtime error: table index is nil

The following error is visible in nginx logs when trying to set value in lrucache:

*10 lua entry thread aborted: runtime error: /usr/share/lua/5.1/resty/lrucache.lua:223: table index is nil

Code leading to the error:

  access_by_lua_block {

    local lrucache = require "resty.lrucache"
    local cache, cache_init_err = lrucache.new(10)

    if not cache or cache_init_err then
        log(ERROR, "Failed to create cache. Reason: " .. (cache_init_err or "unknown"))
    else
        cache:set("dog", 32)
    end
  }

lua-resty-lrucache ver.: 0.08

Start with resty/lrucache.lua at line 223 and trace the cache:set("dog", 32) call from the reported access_by_lua_block. Reproduce the failure with lua-resty-lrucache 0.08 and determine what causes the nil table index; done means the example no longer raises the reported runtime error and the relevant behavior is covered by the project’s tests.