AngularJS: ui-select accept string instead of array

Using angularjs here.

I am using ui-select for allowing the user to select multiple values as:

<div class="form-group" ng-repeat="(name, data) in usersets" ng-class="{ 'has-error': form[inputName + $index].$invalid && submitted }">
   <ui-select name="{{inputName + $index}}" class="btn m-grid-col-md-3" ng-model="data.value" theme="bootstrap">
        <ui-select-match placeholder="data">{{data.value}}</ui-select-match>
        <ui-select-choices repeat="data in data.userValue | filter: $select.search track by $index">
            <div ng-bind-html="data"></div>
        </ui-select-choices>
    </ui-select>
</div>  

I have used the below line to bind the UI select to an array so that it can show all set of options when user starts to type in it.

<ui-select-choices repeat="data in data.userValue | filter: $select.search track by $index">

My issue is because some changes data.userValue above is not returning an array but just a single string value.

If I try to use the same code above I get error on console as:

[ui.select:items] Expected an array but got 'myString'

'myString' is the string returned from data.userValue

Could anyone point me as to what changes do I need to make above to make it accept a single string instead of an array.

Thanks