for angular 9 i changed in this file and it resolved. node_modules\jqwidgets-ng\__ivy_ngcc__\fesm2015\jqwidgets-ng-jqxinput.js
writeValue(value) {
if (this.widgetObject && value) {
if (this.initialLoad) {
setTimeout(_ => this.host.jqxInput('val', value));
this.initialLoad = false;
}
this.host.jqxInput('val', value);
} <strong>else { // this else added by Syntaxmatic Technologies
this.host.jqxInput('val', '');
}</strong>
}