docs: def read_file(file_path, filename=None):
      """ Open file by path and optional filename
  
      If no file name is given the path is interpreted as direct path to the file to be read.
      If there is no file at location the return value will be None to offer a option for case handling.
  
      :param str file_path: Path string.
      :param str filename: File name of the file to be read.
      :return: None or str
      """
      file_path = os.path.realpath(file_path)
      if filename:
          file_path = os.path.join(file_path, filename)
  
      file_content = None
      if os.path.isfile(file_path):
          with open(file_path, 'r') as file_pointer:
              file_content = file_pointer.read()
  
      return file_content