fix: Grid.isMultiSort() will now return true when appropriate (#2298)

Author: sosa-vaadin

vaadin-grid-flow-parent/vaadin-grid-flow/src/main/java/com/vaadin/flow/component/grid/Grid.java

@@ -3093,7 +3093,10 @@ public void setMultiSort(boolean multiSort) {
      */
     public boolean isMultiSort() {
         String multiSort = getElement().getAttribute("multi-sort");
-        return multiSort == null ? false : Boolean.valueOf(multiSort);
+        if (multiSort != null && multiSort.length() == 0) {
+            multiSort = "true";
+        }
+        return Boolean.parseBoolean(multiSort);
     }
 
     @ClientCallable

vaadin-grid-flow-parent/vaadin-grid-flow/src/test/java/com/vaadin/flow/component/grid/GridSortingTest.java

@@ -263,6 +263,23 @@ public void template_renderer_non_comparable_property() {
                 grid.getDataCommunicator().getBackEndSorting());
     }
 
+    @Test
+    public void checkMultiSortDefaultValue() {
+        Assert.assertFalse(grid.isMultiSort());
+    }
+
+    @Test
+    public void checkMultiSortFalse() {
+        grid.setMultiSort(false);
+        Assert.assertFalse(grid.isMultiSort());
+    }
+
+    @Test
+    public void checkMultiSortTrue() {
+        grid.setMultiSort(true);
+        Assert.assertTrue(grid.isMultiSort());
+    }
+
     private void setTestSorting() {
         JsonArray sortersArray = Json.createArray();
         sortersArray.set(0, createSortObject(getColumnId(nameColumn), "asc"));