azure-cli: `az network vnet-gateway vpn-client show-url` unhandled exception

Describe the bug

Command Name az network vnet-gateway vpn-client show-url

Errors:

'str' object has no attribute 'get'
Traceback (most recent call last):
python3.7/site-packages/knack/cli.py, ln 206, in invoke
    cmd_result = self.invocation.execute(args)
cli/core/commands/__init__.py, ln 578, in execute
    raise ex
cli/core/commands/__init__.py, ln 636, in _run_jobs_serially
    results.append(self._run_job(expanded_arg, cmd_copy))
cli/core/commands/__init__.py, ln 629, in _run_job
    six.reraise(*sys.exc_info())
...
site-packages/msrestazure/polling/arm_polling.py, ln 262, in get_status_from_resource
    status = self._get_provisioning_state(response)
site-packages/msrestazure/polling/arm_polling.py, ln 186, in _get_provisioning_state
    return body.get("properties", {}).get("provisioningState")
AttributeError: 'str' object has no attribute 'get'

To Reproduce:

Steps to reproduce the behavior:

• Create a VPN gateway, run az network vpn-gateway vpn-client generate -g xxx -n yyy
• Run az network vnet-gateway vpn-client show-url -g xxx -n yyy

Expected Behavior

Don’t fail with an unhandled exception.

Environment Summary

Darwin-18.6.0-x86_64-i386-64bit
Python 3.7.4
Shell: bash

azure-cli 2.0.69 *

Extensions:
aks-preview 0.4.6

Additional Context