{RDBMS} az postgres flexible-server list: adding a null check to see …

…if resource group passed is already null (#30304)

Co-authored-by: Matthew Boentoro <[email protected]>

src/azure-cli/azure/cli/command_modules/rdbms/validators.py

@@ -824,8 +824,15 @@ def _pg_storage_type_validator(storage_type, auto_grow, high_availability, geo_r
 
 
 def check_resource_group(resource_group_name):
+    # check if rg is already null originally
+    if (not resource_group_name):
+        return False
+
+    # replace single and double quotes with empty string
     resource_group_name = resource_group_name.replace("'", '')
     resource_group_name = resource_group_name.replace('"', '')
+
+    # check if rg is empty after removing quotes
     if (not resource_group_name):
         return False
     return True