Set value problems optionset field ( picklist ) as null

In this new version of CRM -type optionset ( picklist ) fields when sending a value and then finish running the OnChange code that field , the OnChange running again generating a cycle. OnChange code field is this:

function new_workaroundonchange() {
    if (Xrm.Page.getAttribute("new_name").getValue() == null) {
        alert("You must select the name of the person first.");
        Xrm.Page.getAttribute("new_pk1").setValue(null);
    };
};

This is the field:

I appreciate if someone can help me with this case.