az upgrade error

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

## Describe the bug

**Command Name**
`az upgrade`

**Errors:**
```
The command failed with an unexpected error. Here is the traceback:
Expecting value: line 1 column 1 (char 0)
Traceback (most recent call last):
File "/anaconda/envs/azureml_py38/lib/python3.8/site-packages/knack/cli.py", line 231, in invoke
cmd_result = self.invocation.execute(args)
File "/anaconda/envs/azureml_py38/lib/python3.8/site-packages/azure/cli/core/commands/__init__.py", line 663, in execute
raise ex
File "/anaconda/envs/azureml_py38/lib/python3.8/site-packages/azure/cli/core/commands/__init__.py", line 726, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
File "/anaconda/envs/azureml_py38/lib/python3.8/site-packages/azure/cli/core/commands/__init__.py", line 697, in _run_job
result = cmd_copy(params)
File "/anaconda/envs/azureml_py38/lib/python3.8/site-packages/azure/cli/core/commands/__init__.py", line 333, in __call__
return self.handler(*args, **kwargs)
File "/anaconda/envs/azureml_py38/lib/python3.8/site-packages/azure/cli/core/commands/command_operation.py", line 121, in handler
return op(**command_args)
File "/anaconda/envs/azureml_py38/lib/python3.8/site-packages/azure/cli/command_modules/util/custom.py", line 158, in upgrade_version
version_json = json.loads(version_result)
File "/anaconda/envs/azureml_py38/lib/python3.8/json/__init__.py", line 357, in loads
return _default_decoder.decode(s)
File "/anaconda/envs/azureml_py38/lib/python3.8/json/decoder.py", line 337, in decode
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
File "/anaconda/envs/azureml_py38/lib/python3.8/json/decoder.py", line 355, in raw_decode
raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

```

## 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 upgrade`

## Expected Behavior

## Environment Summary
```
Linux-5.4.0-1083-azure-x86_64-with-glibc2.10, Ubuntu 18.04.6 LTS
Python 3.8.5
Installer: PIP

azure-cli 2.38.0

Extensions:
ml 2.6.0

Dependencies:
msal 1.18.0b1
azure-mgmt-resource 21.1.0b1
```
## Additional Context