使用关联数组计算 Lua 的总值数量

我想要统计每个 Redis 键的数据类型，我写了以下代码，但是出现了错误，怎么修复呢？

local detail = {}
detail.hash = 0
detail.set = 0
detail.string = 0

local match = redis.call('KEYS','*')

for i,v in ipairs(match) do
     local val = redis.call('TYPE',v)
     detail.val = detail.val + 1
end

return detail

(error) ERR Error running script (call to f_29ae9e57b4b82e2ae1d5020e418f04fcc98ebef4): @user_script:10: user_script:10: attempt to perform arithmetic on field 'val' (a nil value)