Unclear error if decimal is passed into box.cfg

Tarantool 2.8.2

tarantool> box.cfg{iproto_threads = require('decimal').new(2)}
---
- error: 'builtin/box/load_cfg.lua:19: builtin/box/load_cfg.lua:512: incorrect value
    to convert to decimal as 2 argument'
...

tarantool> box.cfg{memtx_memory = require('decimal').new(2)}
---
- error: 'builtin/box/load_cfg.lua:19: builtin/box/load_cfg.lua:512: incorrect value
    to convert to decimal as 2 argument'
...