Fix: Attendee endpoint serving none values for non-required fields

[akshat0047]

Describe the bug
On rendering attendee information on frontend there are fields with labels but no value we need to fix it by serving only not null value to front end

To Reproduce
Steps to reproduce the behavior:

1. Create an Event on Frontend and add tickets
2. Make attendee form with mixed, required and non required values
3. Buy few tickets with mixed information and check attendees under tickets tab of manage events
4. You will see labels with blank values

Frontend Screenshot

Expected behavior
Labels with blank values should not exist, if a field is blank do not serve it through api
We may fix it by:

• Adding a default value to non required-fields

Additional context
For more refer to this PR and this issue

Working on it

[akshat0047]

@iamareebjamal @prateekj117 I think setting a default value will be a better solution with "Not Specified" ?

[iamareebjamal]

Default value should be saved when saving in DB, not when returning in the API

[iamareebjamal]

Not sure what's the use case, but if there is in future, we can easily handle it in frontend instead