Fix lag

edit-mode/function/restActivityLink.js

@@ -162,10 +162,14 @@ var dp = gantt.createDataProcessor(function(entity, action, data, id) {
                     }
                 });
             }
-            data['duration'] = gantt.calculateDuration({
-                start_date: new Date(data['start_date']),
-                end_date: new Date(data['end_date'])
-            });
+            let newStart = new Date(data['start_date']);
+            let newEnd = new Date(data['end_date']);
+            if (data['start_date'] && data['end_date']) {
+                data['duration'] = gantt.calculateDuration({
+                    start_date: newStart,
+                    end_date: newEnd
+                });   
+            }
             data['geom'] = geom.find(obj => obj.activity_id == id)?.geom;
             return gantt.ajax.put({
                 headers: {