When import a csv without specifying the priority to a project where the priority is optional, the default value is not auto added when the issue was created.

However, in the documentation it was mentioned that the first priority will be used as the priority of created issue if not specified:

If not specified in your CSV file, imported issues will be given the default (i.e. first) Priority as specified in your JIRA system Defining 'Priority' Field Values. You can also create new JIRA values on-the-fly during the import process.

Furthermore, it doesn't throw any exception or add the default value even and JIRA is not really to handle null priorities.

Steps to reproduce

1. Create a project
2. Change its field configurations so 'priority' is optional
3. Use CSV import to import a file where priority is not set

Expected behavior

1. Issues are imported and priority is set as default

Actual behavior

1. Issues are imported without priority

Workaround:

Workaround 1
Search those issues that without priority and bulk edit them so that they will have priority.

Workaround 2
Change the field configuration in your project to have 'priority' as required before importing. You can change it back after the import.