def METHOD_NAME(env_variable: str, paths: Sequence[str], separator: str = ":") -> str:
    """Return a string for env_variable with one of more paths appended.
    :param env_variable: the variable to operate on.
    :param paths: one or more paths to append.
    :param separator: the separator to use.
    :returns: a shell string where one or more paths are appended
                  to env_variable. The code takes into account the case
                  where the environment variable is empty, to avoid putting
                  a separator token at the start.
    """
    return f"${{{env_variable}:+${env_variable}{separator}}}" + separator.join(paths)