fix some issues

lib/ui/grid/column.js

@@ -312,7 +312,9 @@ export class GridDateColumn extends GridColumn {
 
     static setValue(element, val) {
         if (element.tagName === 'INPUT') {
-            if (isNaN(val)) {
+            if (val === '') {
+                element.value = '';
+            } else if (isNaN(val)) {
                 if (/^\d{4}-\d{2}-\d{2}$/.test(val)) {
                     element.value = val;
                 } else if (/^\d{1,2}\/\d{1,2}\/\d{4}$/.test(val)) {