the start does not work when the duration is passed as empty

[marwa-benhassine]

Describe the bug

the start does not work when the duration is passed as empty

To Reproduce Steps to reproduce the behavior:

1. Go to the room page
2. Click the start button

Expected behavior

BigBluebutton parameters should accept nullable values

Screenshots

If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

OS: Windows

Browser: Chrome/Edge/Firefox