diff --git a/filter.php b/filter.php
index e3f67fb..e7860b3 100644
--- a/filter.php
+++ b/filter.php
@@ -342,7 +342,7 @@ function filter_generico_callback(array $link) {
                 }
             }
             //if we have a propname and a propvalue, do the replace
-            if (!empty($courseprop) && !empty($propvalue)) {
+            if (!empty($courseprop) && !is_null($propvalue)) {
                 $genericotemplate = str_replace('@@COURSE:' . $courseprop_allcase . '@@', $propvalue, $genericotemplate);
                 $dataset_vars = str_replace('@@COURSE:' . $courseprop_allcase . '@@', $propvalue, $dataset_vars);
                 $alternate_content = str_replace('@@COURSE:' . $courseprop_allcase . '@@', $propvalue, $alternate_content);