def _resolve_file(file_name):
    """
    Checks if the file exists.

    If the file exists, the method returns its absolute path.
    Else, it returns None

    :param file_name: The name of the file to check
    :return: An absolute path, or None
    """
    if not file_name:
        return None

    path = os.path.realpath(file_name)
    if os.path.isfile(path):
        return path

    return None