Handle null case for SslEnabled flag in App config page

[santhoshb-msft]

Describe the bug A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior:

1. Go Admin portal and Clear out Sslenabled field
2. Clear the field and save
3. Observe Error: Null reference exception

Expected behavior A clear and concise description of what you expected to happen.

Screenshots If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):

• Are you using the CloudShell?
• If not using the CloudShell:
  • OS: [e.g. iOS]
  • PowerShell version
  • Modules installed

Additional context Add any other context about the problem here.