Prevent from empty 'class' attribute in generated html

program/include/rcmail_html_page.php

@@ -70,7 +70,7 @@ class rcmail_html_page extends rcmail_output_html
      */
     public function register_inline_warning($text, $button_label = null, $button_url = null)
     {
-        $text = html::span('', $text);
+        $text = html::span(null, $text);
 
         if ($button_label) {
             $onclick = "location.href = '$button_url'";

program/steps/mail/show.inc

@@ -244,7 +244,7 @@ function rcmail_remote_objects_msg()
     $attrib['class'] = 'notice';
     $attrib['style'] = 'display: none';
 
-    $msg = html::span('', rcube::Q($RCMAIL->gettext('blockedresources'))) . ' '
+    $msg = html::span(null, rcube::Q($RCMAIL->gettext('blockedresources'))) . ' '
         . html::a(array(
             'href'    => "#loadremote",
             'onclick' => rcmail_output::JS_OBJECT_NAME.".command('load-remote')"
@@ -283,7 +283,7 @@ function rcmail_message_buttons()
     $attrib['id']    = 'message-buttons';
     $attrib['class'] = 'notice';
 
-    $msg = html::span('', rcube::Q($RCMAIL->gettext('isdraft'))) . ' ';
+    $msg = html::span(null, rcube::Q($RCMAIL->gettext('isdraft'))) . ' ';
     $msg .= html::a(array(
             'href'    => "#edit",
             'onclick' => rcmail_output::JS_OBJECT_NAME.".command('edit')"