diff --git a/mimemail.rules.inc b/mimemail.rules.inc
index 6f11837..6a8bf32 100644
--- a/mimemail.rules.inc
+++ b/mimemail.rules.inc
@@ -32,30 +32,35 @@ function mimemail_rules_action_info() {
           'label' => t('CC Recipient'),
           'description' => t("The mail's carbon copy address. You may separate multiple addresses with comma."),
           'optional' => TRUE,
+          'allow null' => TRUE,
         ),
         'bcc' => array(
           'type' => 'text',
           'label' => t('BCC Recipient'),
           'description' => t("The mail's blind carbon copy address. You may separate multiple addresses with comma."),
           'optional' => TRUE,
+          'allow null' => TRUE,
         ),
         'from_name' => array(
           'type' => 'text',
           'label' => t('Sender name'),
           'description' => t("The sender's name. Leave it empty to use the site-wide configured name."),
           'optional' => TRUE,
+          'allow null' => TRUE,
         ),
         'from_mail' => array(
           'type' => 'text',
           'label' => t('Sender e-mail address'),
           'description' => t("The sender's address. Leave it empty to use the site-wide configured address."),
           'optional' => TRUE,
+          'allow null' => TRUE,
         ),
         'reply_to' => array(
           'type' => 'text',
           'label' => t('Reply e-mail address'),
           'description' => t("The address to reply to. Leave it empty to use the sender's address."),
           'optional' => TRUE,
+          'allow null' => TRUE,
         ),
         'list_unsubscribe' => array(
           'type' => 'text',
@@ -128,12 +133,14 @@ function mimemail_rules_action_info() {
           'label' => t('Sender name'),
           'description' => t("The sender's name. Leave it empty to use the site-wide configured name."),
           'optional' => TRUE,
+          'allow null' => TRUE,
         ),
         'from_mail' => array(
           'type' => 'text',
           'label' => t('Sender e-mail address'),
           'description' => t("The sender's address. Leave it empty to use the site-wide configured address."),
           'optional' => TRUE,
+          'allow null' => TRUE,
         ),
         'subject' => array(
           'type' => 'text',