zone import fails

### **This is autogenerated. Please review and update as needed.**

## Describe the bug
This occurs on any machine i try to import a zone file with.
**Command Name**
`az network private-dns zone import`

**Errors:**
```
The command failed with an unexpected error. Here is the traceback:
argument of type 'NoneType' is not iterable
Traceback (most recent call last):
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\knack/cli.py", line 231, in invoke
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/core/commands/__init__.py", line 657, in execute
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/core/commands/__init__.py", line 720, in _run_jobs_serially
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/core/commands/__init__.py", line 691, in _run_job
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/core/commands/__init__.py", line 328, in __call__
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/core/commands/command_operation.py", line 121, in handler
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/command_modules/privatedns/custom.py", line 47, in import_zone
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/command_modules/network/zone_file/parse_zone_file.py", line 415, in parse_zone_file
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/command_modules/network/zone_file/parse_zone_file.py", line 305, in _add_record_names
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/command_modules/network/zone_file/parse_zone_file.py", line 205, in _serialize
TypeError: argument of type 'NoneType' is not iterable

```

## To Reproduce:
Steps to reproduce the behavior. Note that argument values have been redacted, as they may contain sensitive information.

- _Put any pre-requisite steps here..._
- `az network private-dns zone import -g {} -n {} -f {}`

## Expected Behavior

## Environment Summary
```
Windows-10-10.0.19041-SP0
Python 3.8.9
Installer: MSI

azure-cli 2.28.0

Extensions:
application-insights 0.1.13

```
## Additional Context