Error "runtime error: invalid memory address or nil pointer dereference" what is the problem?

Question

go

The error is displayed runtime error: invalid memory address or nil pointer dereference
Approximately at the moment

item_sheet_ln, ok = ln_sheet[ArrMid[i]]
    if r.Is_factor {
      vale *= item_sheet_ln.Factor
    }

Answer 1

Check what ArrMid[i]exists and what is item_sheet_lnnot nil.
In principle, nil can ber.Is_factor