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module.js

@@ -45,18 +45,23 @@ M.mod_programming.init_history = function(Y) {
     var r = Y.all('.diff1');
     if (r.size() > 0) {
         var firstDiff = r.item(0);
-        if (firstDiff) {
+        if (firstDiff && firstDiff.hide) {
             firstDiff.hide();
         }
     }
     r = Y.all('.diff2');
     if (r.size() > 0) {
         var lastDiff = r.item(r.size() - 1);
-        if (lastDiff) {
+        if (lastDiff && lastDiff.hide) {
             lastDiff.hide();
         }
     }
 
+    var historyForm = Y.one('#history-diff-form');
+    if (!historyForm) {
+        return;
+    }
+
     var is_history_diff_form_submitable = function() {
         var f1 = false, f2 = false;
         Y.all('.diff1').each(function(node) {
@@ -71,11 +76,14 @@ M.mod_programming.init_history = function(Y) {
         return f1 && f2 && f1.get('value') != f2.get('value');
     };
 
-    Y.one('#history-diff-form').on('submit', is_history_diff_form_submitable);
+    historyForm.on('submit', is_history_diff_form_submitable);
 
-    Y.all('#history-diff-form input[type=radio]').each(function(node) {
+    historyForm.all('input[type=radio]').each(function(node) {
         node.on('change', function() {
-            var btn = Y.one('#history-diff-form input[type=submit]');
+            var btn = historyForm.one('input[type=submit]');
+            if (!btn) {
+                return;
+            }
             if (is_history_diff_form_submitable()) {
                 btn.removeAttribute('disabled');
             } else {
@@ -84,7 +92,10 @@ M.mod_programming.init_history = function(Y) {
         });
     });
 
-    Y.one('#history-diff-form input[type=submit]').setAttribute('disabled', true);
+    var submitBtn = historyForm.one('input[type=submit]');
+    if (submitBtn) {
+        submitBtn.setAttribute('disabled', true);
+    }
 };
 
 M.mod_programming.init_reports_detail = function(Y) {