Fixed #3967 - DataTable:When using ColumnGroup in a table with more than two frozen columns

components/lib/datatable/HeaderCell.vue

@@ -294,10 +294,12 @@ export default {
                 if (filterRow) {
                     let index = DomHandler.index(this.$el);
 
+                    if (filterRow.children[index]) {
                         filterRow.children[index].style.left = this.styleObject.left;
                         filterRow.children[index].style.right = this.styleObject.right;
                     }
                 }
+            }
         },
         onHeaderCheckboxChange(event) {
             this.$emit('checkbox-change', event);