az aro create error AttributeError: 'NoneType' object has no attribute 'lower'

### Describe the bug

During the az aro create command the following error occu's

The command failed with an unexpected error. Here is the traceback:
'NoneType' object has no attribute 'lower'
Traceback (most recent call last):
File "/usr/lib64/az/lib/python3.9/site-packages/knack/cli.py", line 233, in invoke
cmd_result = self.invocation.execute(args)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/__init__.py", line 663, in execute
raise ex
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/__init__.py", line 726, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/__init__.py", line 697, in _run_job
result = cmd_copy(params)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/__init__.py", line 333, in __call__
return self.handler(*args, **kwargs)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/command_operation.py", line 121, in handler
return op(**command_args)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/custom.py", line 82, in aro_create
validate(cmd,
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/custom.py", line 252, in validate
error_obj = error_func(cmd, namespace)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/_dynamic_validators.py", line 115, in inner
errors = func(cmd, namespace)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/_dynamic_validators.py", line 295, in _validate_resource_permissions
resource_contributor_exists = has_role_assignment_on_resource(cmd.cli_ctx,
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/_rbac.py", line 73, in has_role_assignment_on_resource
assignment.principal_id.lower() == object_id.lower():
AttributeError: 'NoneType' object has no attribute 'lower'

### Related command

az aro create

### Errors

The command failed with an unexpected error. Here is the traceback:
'NoneType' object has no attribute 'lower'
Traceback (most recent call last):
File "/usr/lib64/az/lib/python3.9/site-packages/knack/cli.py", line 233, in invoke
cmd_result = self.invocation.execute(args)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/__init__.py", line 663, in execute
raise ex
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/__init__.py", line 726, in _run_jobs_serially
results.append(self._run_job(expanded_arg, cmd_copy))
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/__init__.py", line 697, in _run_job
result = cmd_copy(params)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/__init__.py", line 333, in __call__
return self.handler(*args, **kwargs)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/core/commands/command_operation.py", line 121, in handler
return op(**command_args)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/custom.py", line 82, in aro_create
validate(cmd,
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/custom.py", line 252, in validate
error_obj = error_func(cmd, namespace)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/_dynamic_validators.py", line 115, in inner
errors = func(cmd, namespace)
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/_dynamic_validators.py", line 295, in _validate_resource_permissions
resource_contributor_exists = has_role_assignment_on_resource(cmd.cli_ctx,
File "/usr/lib64/az/lib/python3.9/site-packages/azure/cli/command_modules/aro/_rbac.py", line 73, in has_role_assignment_on_resource
assignment.principal_id.lower() == object_id.lower():
AttributeError: 'NoneType' object has no attribute 'lower'

### Issue script & Debug output

az aro create \
--resource-group $AZR_RESOURCE_GROUP \
--name $AZR_CLUSTER \
--vnet "$AZR_CLUSTER-aro-vnet-$AZR_RESOURCE_LOCATION" \
--master-subnet "$AZR_CLUSTER-aro-control-subnet-$AZR_RESOURCE_LOCATION" \
--worker-subnet "$AZR_CLUSTER-aro-machine-subnet-$AZR_RESOURCE_LOCATION" \
--pull-secret @$AZR_PULL_SECRET \
--cluster-resource-group $AZR_RESOURCE_GROUP_INFRA \
--client-id $AZR_CLIENT_ID \
--client-secret $AZR_SECRET_VALUE \
--worker-vm-size $AZR_WORKER_SIZE \
--worker-count $AZR_WORKER_COUNT

### Expected behavior

cluster created

### Environment Summary

azure-cli 2.54.0

core 2.54.0
telemetry 1.1.0

Extensions:
ai-examples 0.2.5
ml 2.21.1
ssh 2.0.2

Dependencies:
msal 1.24.0b2
azure-mgmt-resource 23.1.0b2

Python location '/usr/bin/python3.9'
Extensions directory '/home/maarten_brouwers1/.azure/cliextensions'
Extensions system directory '/usr/lib/python3.9/site-packages/azure-cli-extensions'

Python (Linux) 3.9.14 (main, Oct 12 2023, 19:48:32)
[GCC 11.2.0]

Legal docs and information: aka.ms/AzureCliLegal

Your CLI is up-to-date.

### Additional context

_No response_