diff
<       else if (!join_lines && *col_sep_string == '\t') // In this case, col_sep_length must be 1.
---
>       else if (!join_lines && col_sep_string) {
>           if (*col_sep_string != '\t' || col_sep_length != 1) {
>               fprintf(stderr, "Error: Invalid column separator configuration.\n");
>               return;
>           }
>       }
