[Fix] - Added handling when assigning vm identities

Author: william051200

src/azure-cli/azure/cli/command_modules/vm/custom.py

@@ -880,7 +880,7 @@ def setter(vm, external_identities=external_identities):
                 command_args['mi_user_assigned'].append(key)
 
         if identity.get('userAssignedIdentities'):
-            for key in identity.get('userAssignedIdentities').keys():
+            for key in identity.get('userAssignedIdentities', {}).keys():
                 if key not in command_args['mi_user_assigned']:
                     command_args['mi_user_assigned'].append(key)