Minor - Add default value to default value setting in create_course_extra_field() and create_session_extra_field()

main/inc/lib/course.lib.php

@@ -2922,11 +2922,10 @@ class CourseManager
      * @param    string    Field's internal variable name
      * @param    int        Field's type
      * @param    string    Field's language var name
-     * @param integer $fieldType
      * @param string $default
      * @return boolean     new extra field id
      */
-    public static function create_course_extra_field($variable, $fieldType, $displayText, $default)
+    public static function create_course_extra_field($variable, $fieldType, $displayText, $default = '')
     {
         $extraField = new ExtraField('course');
         $params = [

main/inc/lib/sessionmanager.lib.php

@@ -2619,7 +2619,7 @@ class SessionManager
      * @param   string  $default    Field's default value
      * @return int     new extra field id
      */
-    public static function create_session_extra_field($variable, $fieldType, $displayText, $default)
+    public static function create_session_extra_field($variable, $fieldType, $displayText, $default = '')
     {
         $extraField = new ExtraFieldModel('session');
         $params = [