Index: views_handler_field.inc
===================================================================
--- views_handler_field.inc
+++ views_handler_field.inc
@@ -247,7 +247,15 @@
  */
 class views_handler_field_file_size extends views_handler_field {
   function render($values) {
-    return format_size($values->{$this->field_alias});
+    // MODIF : do not try to format a NULL size.
+    //return format_size($values->{$this->field_alias});
+    if ($values->{$this->field_alias}) {
+      return format_size($values->{$this->field_alias});
+    }
+    else {
+      return '';
+    }
+    // /MODIF
   }
 }