Help text on signup settings contains broken link on new nodes

When you create a new node, that is signup-enabled by default, you end up with a broken link to the "Signups" tab since there's no nid yet:

  $hint = t('If enabled, you can control whether users may sign up by visiting the !signups tab and toggling if signups are %open or %closed for this @node_type.', array('!signups' => l(t('Signups'), 'node/'. $node->nid .'/signups'), '%open' => t('open'), '%closed' => t('closed'), '@node_type' => strtolower(node_get_types('name', $form['type']['#value']))));

$node is NULL on new issues, so we get a PHP warning and a broken link.