attempt to perform arithmetic on a nil value

The problem

The console shows "attempt to perform arithmetic on a nil value" and the script breaks right on an addition, subtraction or multiplication.

The cause

One of the operands is nil: a Config value that doesn't exist, a database query that returned no row, or a typo in the variable name.

The solution

Validate the value before operating and give it a default:

-- BAD: if Config.Precio is nil, it crashes
local total = Config.Precio * cantidad

-- GOOD: default value + clear warning
local precio = Config.Precio or 0
if precio == 0 then
    print('^3[mi_recurso] Config.Precio is not defined^0')
end
local total = precio * cantidad

Step by step

1. 1.Look at the file and line the console points to: that's where the operation is.
2. 2.Check that every variable in the operation has a value (Config, MySQL result, event parameter).
3. 3.Use `variable or 0` for numbers that might be missing.
4. 4.If it comes from the database, make sure the query returned a row before using the data.

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