code: def config_txt_to_string(string):
      
      if string is None:
          return None
      pairs = [l.strip() for l in string.splitlines() if len(l.strip()) > 0]
      return gc.CONFIG_STRING_SEPARATOR_SYMBOL.join(pairs)
docs: Convert the contents of a TXT config file
      into the corresponding configuration string ::
  
          key_1=value_1|key_2=value_2|...|key_n=value_n
  
      Leading and trailing blank characters will be stripped
      and empty lines (after stripping) will be ignored.
  
      :param string string: the contents of a TXT config file
      :rtype: string