'NoneType' object has no attribute 'private_dns_zone_configs'

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

## Describe the bug

**Command Name**
`az network private-endpoint dns-zone-group add`

**Errors:**
```
The command failed with an unexpected error. Here is the traceback:
'NoneType' object has no attribute 'private_dns_zone_configs'
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 658, in execute
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/core/commands/__init__.py", line 721, in _run_jobs_serially
File "D:\a\1\s\build_scripts\windows\artifacts\cli\Lib\site-packages\azure/cli/core/commands/__init__.py", line 692, 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/network/custom.py", line 3415, in add_private_endpoint_private_dns_zone
AttributeError: 'NoneType' object has no attribute 'private_dns_zone_configs'

```

## 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-endpoint dns-zone-group add --endpoint-name {} --resource-group {} --name {} --zone-name {} --subscription {} --private-dns-zone {}`

## Expected Behavior

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

azure-cli 2.34.1 *

Extensions:
costmanagement 0.2.1

Dependencies:
msal 1.16.0
azure-mgmt-resource 20.0.0
```
## Additional Context