def as_formatted_lines(lines):
    """
    Return a text formatted for use in a Debian control file with proper
    continuation for multilines.
    """
    if not lines:
        return ''
    formatted = []
    for line in lines:
        stripped = line.strip()
        if stripped:
            formatted.append(' ' + line)
        else:
            formatted.append(' .')
    return '\n'.join(formatted).strip()