fix: handling of empty values in NcDateTimePickerNative

Signed-off-by: Richard Steinmetz <richard@steinmetz.cloud>

src/components/NcDateTimePickerNative/NcDateTimePickerNative.vue

@@ -2,6 +2,7 @@
   - @copyright Copyright (c) 2022 Julia Kirschenheuter <julia.kirschenheuter@nextcloud.com>
   -
   - @author Julia Kirschenheuter <julia.kirschenheuter@nextcloud.com>
+  - @author Richard Steinmetz <richard@steinmetz.cloud>
   -
   - @license GNU AGPL version 3 or any later version
   -
@@ -163,10 +164,11 @@ export default {
 		 * The date is – like the `Date` object in JavaScript – tied to UTC.
 		 * The selected time zone does not have an influence of the selected time and date value.
 		 * You have to translate the time yourself when you want to factor in time zones.
+		 * Pass null to clear the input field.
 		 */
 		value: {
 			type: Date,
-			required: true,
+			default: null,
 		},
 
 		/**
@@ -265,7 +267,7 @@ export default {
 						 *
 						 * @return {string} empty string
 						 */
-						return this.$emit('input', '')
+						return this.$emit('input', null)
 					}
 					if (this.type === 'time') {
 						const time = $event.target.value