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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def plugin(plugin_key=None):
 """ Serve plugin page :param plugin_key: Which plugin page to server; if None -> landing page (default: None) :type plugin_key: None | unicode """

    p = None
    if plugin_key:
        try:
            p = db_plugin_instance.plugin_get(plugin_key)
        except KeyError:
            logger.error(u"Plugin '{}' not found".format(plugin_key))

    return render_template("plugin.html", title="Plugins", plugin=p)