How do I fix the error "private method 'split' called for nil:NilClass" during custom import?

During a custom import, the error failed: private method ‘split’ called for nil:NilClass can appear when you upload the CSV file.

Cause

The uploaded CSV file contains data in columns other than the header columns that were in the CSV file generated by myschool.

Solution

1. Open the CSV file generated for the import.
2. Make sure data is entered only in the columns that already have headers in the generated file.
3. Remove any content from extra columns beyond those in the template, then save the file.
4. Upload the file again.

For more help, see How to perform a custom import and CSV file guide for custom import.