def METHOD_NAME():
    modified_files = find_modified_files_against_master_branch()
    if len(modified_files) == 1 and contain_index_json(modified_files):
        # Scenario 1.
        # This scenarios is for modify index.json only.
        # If the modified metadata items refer to the extension code exits in this repo, PR is be created via Pipeline.
        # If the modified metadata items refer to the extension code doesn't exist, PR is created from Service Team.
        # We try to verify linter on it.
        linter_on_external_extension(modified_files[0])
    else:
        # modified files contain more than one file
        if contain_extension_code(modified_files):
            # Scenario 2, we reject.
            if contain_index_json(modified_files):
                raise ModifiedFilesNotAllowedError()
            linter_on_internal_extension(modified_files)
        else:
            separator_line()
            print('no extension source code modified, no extension needs to be linter')
            separator_line()