Code functioning in JSFiddle enviroment but not when run otherwise

So when working on another question, here, I got a great answer from @earl3s and a link to a jsfiddle of the work and it appeared to work fine but when trying to run it in repl.it it gave me an error, and when trying to run it locally I got an error reading "Uncaught TypeError: Cannot read property 'add' of null" on line 19. I may be submitting them wrong or the code may be written incorrectly, and insight would be appreciated. Here is the origninal code:

<script>
    if (window.location.href.substring(0,9) === "http://ww") {
    var home_var = "bing.com";    
    }
    else if (window.location.href.substring(0,9) === "https://p") {
    var home_var = "https://px.multiscreensite.com/index.php?url=bing.com";
    }
    else {
    var home_var = "1";
    }
    var select= document.getElementById("mySelect");
    var option = document.createElement("option");
    option.text = "Hope Page";
    option.value = home_var;
    select.add(option);
    console.log(home_var);
</script>

<select id="mySelect" OnChange="window.location.href=this.value">
    <option>Tagged Stuff and Navigation</option>
</select>