Steps to reproduce:

• Create a custom user profile field of type menu.
• Leave the "Required" checkbox unchecked.
• Add some options.
• Leave Default blank.
• Attempt to upload a user spreadsheet containing two records. One record has data for the custom field. The next record does not have data for the custom field.

You will be shown an invalid field error in the status when previewing the upload.

Expected Behavior: You should be allowed to leave the field blank in the CSV since the field is marked as optional.