class_docstr: For the "run" command.
class_docstr_tok: ["For","the","``","run","''","command","."]
code: def test_illformed_expression(self):
      parser = cmd_line_parser.CmdLineParser()
      with self.assertRaisesRegex(
          post_process_utils.PostProcessParseError,
          "Cannot have empty post-processing expression",
      ):
          parser.parse_line("| | to_upper")
  
      with self.assertRaisesRegex(
          post_process_utils.PostProcessParseError,
          "Cannot have empty post-processing expression",
      ):
          parser.parse_line("| ")
  
      with self.assertRaisesRegex(
          post_process_utils.PostProcessParseError,
          "Cannot have empty post-processing expression",
      ):
          parser.parse_line("| add_length |")
  
imports: from __future__ import annotations
  import sys
  from unittest import mock
  from absl.testing import absltest
  from google.generativeai.notebook import argument_parser
  from google.generativeai.notebook import cmd_line_parser
  from google.generativeai.notebook import model_registry
  from google.generativeai.notebook import parsed_args_lib
  from google.generativeai.notebook import post_process_utils
  from google.generativeai.notebook.lib import llm_function
  from google.generativeai.notebook.lib import llmfn_output_row
  from google.generativeai.notebook.lib import llmfn_outputs
  from google.generativeai.notebook.lib import model
label_desc: Use image node_id 2 for calling the CmdLineParserPostProcessingTest obj's underlying member method code with example usage: obj.test_illformed_expression() without return types