Don't fetch image if it's not provided - let RP handle this case

Author: jepetty

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

@@ -1574,20 +1574,6 @@ def start_containerappsjob(cmd,
         # If no image is provided, fetch the existing job's image
         if image is not None:
             container_def["image"] = image if not is_registry_msi_system(registry_identity) else HELLO_WORLD_IMAGE
-        else:
-            # Fetch the existing job definition to get the default image
-            try:
-                containerappjob_def = ContainerAppsJobClient.show(cmd=cmd, resource_group_name=resource_group_name, name=name)
-            except Exception as e:
-                handle_raw_exception(e)
-
-            if not containerappjob_def:
-                raise ResourceNotFoundError("The containerapp job '{}' does not exist".format(name))
-
-            existing_image = safe_get(containerappjob_def, "properties", "template", "containers", default=[{}])[0].get("image")
-            if not existing_image:
-                raise ValidationError("Could not find an existing image for the containerapp job '{}'. Please specify --image.".format(name))
-            container_def["image"] = existing_image if not is_registry_msi_system(registry_identity) else HELLO_WORLD_IMAGE
 
         if env_vars is not None:
             container_def["env"] = parse_env_var_flags(env_vars)