def render_header(level_and_content):
    """
    - level_and_content: None OR string OR list of [postive-int, string] OR tuple of
      (positive-int, string), the header level and content
    RETURN: string, the header
    """
    if level_and_content is None:
        return ""
    if isinstance(level_and_content, str):
        level = 1
        content = level_and_content
    elif isinstance(level_and_content, (list, tuple)):
        level, content = level_and_content
        if level < 1:
            level = 1
    else:
        raise Exception("Unhandle type of level_and_content")
    return "#" * level + " " + content + "\n\n"