--- loncom/interface/lonextresedit.pm	2019/05/02 02:12:18	1.28
+++ loncom/interface/lonextresedit.pm	2019/05/02 23:09:39	1.29
@@ -1,7 +1,7 @@
 # The LearningOnline Network
 # Documents
 #
-# $Id: lonextresedit.pm,v 1.28 2019/05/02 02:12:18 raeburn Exp $
+# $Id: lonextresedit.pm,v 1.29 2019/05/02 23:09:39 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -981,12 +981,14 @@ function extUrlPreview(caller,protocol)
             http.onreadystatechange = function() {
                 if (http.readyState == 4) {
                     if (http.status == 200) {
-                        if (http.responseText == 1) {
-                            noiframe = 1;
-                        } else if (http.responseText == -1) {
-                            nopriv = 1;
-                        } else if (http.responseText == 0) {
-                            badurl = 1;
+                        if (http.responseText.length > 0) {
+                            if (http.responseText == 1) {
+                                noiframe = 1;
+                            } else if (http.responseText == -1) {
+                                nopriv = 1;
+                            } else if (http.responseText == 0) {
+                                badurl = 1;
+                            }
                         }
                         openPreviewWindow(url,name,noiframe,mixed,nopriv,badurl);
                     }