Steps to reproduce:

1. Create LLD rule of type Zabbix trapper
2. Create calculated item prototype with formula like "абв"
3. Send LLD JSON:

   $ zabbix_sender -s host -k lld -o '{"data":[{"{#M}":"1"}]}'

1. Wait until discovered item is checked

Result:
Item discovered but then appears error, that formula isn't correct "Cannot evaluate expression: expected numeric token at "абв"."
Expected:
Check the formula before items will be discovered