Adding placeholder to JQuery (AJS.$) MultiSelect Field (Jira, JavaScript)

I have the following code, which has a function converting a Jira Multi-Select Customfield to Autocomplete Renderer: https://confluence.atlassian.com/jirakb/how-to-enable-autocomplete-renderer-for-multi-select-custom-field-in-jira-754978239.html

The Jira context etc. is not so relevant here, however, the only thing I try and fail to achieve is to add a simple placeholder text to the Dropdown. The placeholder should be there when the Dropdown has no value selected.

Can someone help? I can’t imagine it to be that difficult if you are familiar with the syntax.

<script type="text/javascript">
(function($) {
    
    function convertMulti(id){
        if (AJS.$('#'+id+"-textarea").length == 0){
            new AJS.MultiSelect({

                element: $("#"+id),
                itemAttrDisplayed: "label",
                errorMessage: AJS.params.multiselectComponentsError,
                
                
            });
        }
    }
  
    AJS.toInit(function(){ 
        convertMulti("customfield_16043");
        
    })
  
    JIRA.bind(JIRA.Events.NEW_CONTENT_ADDED, function (e, context) {
        AJS.$("#customfield_16043 option[value='-1']").remove();
        convertMulti("customfield_16043");
        
    });
})(AJS.$);



</script>

in the following section of the code snippet, I tried several things to add a placeholder. However, I am not familiar enough with javascript/jquery and I failed to succeed here.

new AJS.MultiSelect({.....})