DateBox: Fix error on value change when empty string is set as initial value (T1301310) (#30542)

Co-authored-by: Ruslan Farkhutdinov <ruslan.farkhutdinov@devexpress.com>

Author: Ruslan Farkhutdinov

packages/devextreme/js/__internal/ui/calendar/m_calendar.ts

@@ -283,7 +283,7 @@ class Calendar<
       return 'number';
     }
 
-    if (!isString(value)) {
+    if (!isString(value) || value === '') {
       return;
     }
 

packages/devextreme/js/__internal/ui/date_box/m_date_box.base.ts

@@ -758,7 +758,7 @@ class DateBox extends DropDownEditor<DateBoxBaseProperties> {
   }
 
   _getSerializationFormat() {
-    const value = this.option('value');
+    const { value } = this.option();
 
     if (this.option('dateSerializationFormat') && config().forceIsoDateParsing) {
       return this.option('dateSerializationFormat');
@@ -768,7 +768,7 @@ class DateBox extends DropDownEditor<DateBoxBaseProperties> {
       return 'number';
     }
 
-    if (!isString(value)) {
+    if (!isString(value) || value === '') {
       return;
     }
 

packages/devextreme/testing/tests/DevExpress.ui.widgets.editors/datebox.tests.js

@@ -2230,14 +2230,14 @@ QUnit.module('datebox w/ calendar', {
         assert.deepEqual(this.fixture.input.val(), dateLocalization.format(date, this.fixture.format));
     });
 
-    QUnit.test('DateBox must pass value to calendar correctly if value is empty string', function(assert) {
+    QUnit.test('DateBox should pass empty string value to calendar if value is empty string', function(assert) {
         this.reinitFixture({
             value: '',
             pickerType: 'calendar',
             opened: true
         });
 
-        assert.equal(this.fixture.dateBox._strategy._widget.option('value'), null, 'value is correctly');
+        assert.equal(this.fixture.dateBox._strategy._widget.option('value'), '', 'value is equal to empty string');
     });
 
     QUnit.test('DateBox must show the calendar with a proper date selected', function(assert) {
@@ -6164,6 +6164,33 @@ QUnit.module('DateBox number and string value support', {
             assert.ok(true, 'there is no error');
         }
     });
+
+    [true, false].forEach(isRuntime => {
+        QUnit.test(`should not throw error after applying new date when empty string ${isRuntime ? 'runtime' : 'initial'} value is passed and datetime type used (T1301310)`, function(assert) {
+            const dateBox = $('#dateBox').dxDateBox({
+                value: isRuntime ? undefined : '',
+                type: 'datetime',
+            }).dxDateBox('instance');
+
+            try {
+                dateBox.open();
+
+                if(isRuntime) {
+                    dateBox.option('value', '');
+                }
+
+                const $calendarCell = $(`.${CALENDAR_CELL_CLASS}`).eq(0);
+                $calendarCell.trigger('dxclick');
+
+                const $applyButton = $(dateBox.content()).parent().find(APPLY_BUTTON_SELECTOR);
+                $applyButton.trigger('dxclick');
+
+                assert.ok(true, 'no error');
+            } catch(e) {
+                assert.ok(false, `error thrown: ${e.message}`);
+            }
+        });
+    });
 });
 
 testModule('native picker', function() {