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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_get(self, plugin_name):
 """ Find plugins in controller :param plugin_name: Name of the plugin to find :type plugin_name: str | None :return: Plugin or None and error message :rtype: (settable_plugin.SettablePlugin | None, str) """

        if not plugin_name:
            return None, u"Plugin name not set"
        for plugin in self.controller.plugins:
            if not isinstance(plugin, SettablePlugin):
                continue
            if plugin.name == plugin_name:
                return plugin, ""
        return None, u"Settable plugin '{}' not found".format(plugin_name)