Unable to properly call a UI Script from a Catalog Client Script.

[RyoyaFukuda]

Hi,all.

I am trying to call a UI Script from a Catalog Client Script.
This development is being done within a custom application.

Here is the script. And error message is ''UI Script  x_16799_test.TestUIScript is loaded but can not find dummyFunction or result is fraud. Result: null'
Could you please tell me why the UI Script cannot be called successfully?

Catalog Client Script
Type : onChange

UI Type : All

function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading || newValue == '') {
        return;
    }

    var value = newValue;
    var name = 'u_int_test';
    var uiScriptName = 'x_16799_test.TestUIScript';


    if (typeof g_ui_scripts !== 'undefined') {
        // Workspace（WEP）
         g_ui_scripts.getUIScript(uiScriptName).then(function(result) {
        if (result && typeof result.dummyFunction === 'function') {
		//  if (result && typeof result.formatAndTruncateNumber === 'function') {
            g_form.addInfoMessage('UI Script ' + uiScriptName + ' is loaded and find dummyFunction');
            result.dummyFunction();
        } else {
            g_form.addInfoMessage('UI Script ' + uiScriptName + ' is loaded but can not find dummyFunction or  result is fraud.  Result: ' + JSON.stringify(result));
        }
    }).catch(function(error) {
        g_form.addErrorMessage('UI script failed to load: ' + error);
    });
    }
}

UI Script
API:x_16799_test.TestUIScript

(function() {
    return {
        dummyFunction: function() {
            // do noting
        }
    };
})();

[RyoyaFukuda]

@Ankur Bawiskar 
I modified the code in the same way as the code described in the knowledge base I received, but I got an error message saying "Cannot read properties of null (reading 'dummyFunction')"