def update_list(content, new_values):
    """Update a list with additional or new values."""
    new_content = content[:] if content else []
    new_values = [x.strip() for x in new_values.split(",")] if isinstance(new_values, str) else new_values or []
    for value in new_values:
        if value == "-":
            new_content.clear()
        elif value and value not in new_content:
            new_content.append(value)
    return new_content