Unable to access the Project Overview/Update plan page when PDF is missing from plan

[jupiter007]

Describe the bug
Problem 1: When a user clicks the "Project name & PDF upload" link from the Plan Overview page, the following Type Error is thrown, "TypeError: Cannot read properties of undefined (reading 'identifier')", due to a missing PDF and the user is not able to progress. We should be adding a null check for "pdf" before trying to using "pdf.identifier".

The error appears to occur in the "get narrative ()" section of models.js on the line "pdf.file_name = pdf.identifier.split('/').pop();".

To Reproduce
Steps to reproduce the behavior:

1. Upload plan and select a plan that does not include a PDF
2. Click on "Project name & PDF upload"
3. Notice the error, as described above

Expected behavior
User should see a form where they can enter the Project name and upload a DMP PDF

Screenshots

[bofstein]

May happen only if a project has related works, like this one: https://dmptool-stg.cdlib.org/dashboard/dmp/doi.org_10.48321_D1912B40EA/pdf