code: def default_properties_file
        # try the current directory
        file = File.expand_path(DEF_PROP_FILE_NM)
        return file if File.exists?(file)
        # try home
        home = ENV['HOME'] || ENV['USERPROFILE'] || '~'
        file = File.expand_path(DEF_PROP_FILE_NM, home)
        file if File.exists?(file)
      end
docs: The default application properties file is determined as follows:
     * +./.catissue+, if it exists
     * +~/.catissue+, otherwise
  
   @return [String, nil] the default application properties file