无法在HTMLSelectElement.onchange上读取null的属性“ origin”

Question

在搜索输出中，有一个下拉框可以更改姓氏的来源。

但是，当您尝试更改选择字段中的值时，出现错误；

Cannot read property 'origin' of null at HTMLSelectElement.onchange

代码在这里；

//functions to parse the querystring
function PageQuery(q) {
    if(q.length > 1) this.q = q.substring(1, q.length);
    else this.q = null;
    this.keyValuePairs = new Array();
    if(q) {
    for(var i=0; i < this.q.split("&").length; i++) {
    this.keyValuePairs[i] = this.q.split("&")[i];
    }
    }
    this.getKeyValuePairs = function() { return this.keyValuePairs; }
    this.getValue = function(s) {
    for(var j=0; j < this.keyValuePairs.length; j++) {
    if(this.keyValuePairs[j].split("=")[0] == s)
    return this.keyValuePairs[j].split("=")[1];
    }
    return false;
    }
    this.getParameters = function() {
    var a = new Array(this.getLength());
    for(var j=0; j < this.keyValuePairs.length; j++) {
    a[j] = this.keyValuePairs[j].split("=")[0];
    }
    return a;
    }
    this.getLength = function() { return this.keyValuePairs.length; } 
}
function queryString(key){
    var page = new PageQuery(window.location.search); 
    return unescape(page.getValue(key)); 
}

function decode(str) {
     return unescape(str.replace(/\+/g, " "));
}


if (queryString("surname")!="" && queryString("surname")!="false"){
    document.write ("<h3>Surname</h3>");
    document.write (queryString("surname"));

    if(queryString("numoforigins") == ""){
        document.write ("<br /><br />The name was not found."); 
    }else{
        document.write ("<h3>Origin</h3>");

        if (queryString("numoforigins") == "1"){
            document.write (queryString("wordorigin"));
        }else{
            document.write ("<select name='origin' onchange='if (this.form.origin.options[this.form.origin.selectedIndex].value) window.location.href=this.form.origin.options[this.form.origin.selectedIndex].value'>");
            document.write ("<option selected>" + queryString("wordorigin") + "</option>"); 
            //loops through all origins and adds to combobox and calls surnameSearch.asp every time the combobox value changes
            for(var i=1; i <= parseInt(queryString("numoforigins")); i++){
                if (queryString("wordorigin") != queryString("originword" + i)) //ensures no duplicate options put into combobox
                    document.write("<option value='https://www.hallofnames.com/services/surnameSearch.asp?Licensee=24010&surname=" + queryString("surname") + "&origin=" + queryString("origin" + i) + "'>" + queryString("originword" + i) + "</OPTION>" );
            }
            document.write (  "</select> (" + queryString("numoforigins") + " origins available)");
        }
        if(queryString("hisdata")!=""  && queryString("hisdata")!="false"){
            document.write ( "<h3>History</h3>");
            document.write (decode(queryString("hisdata")));
        }
        if(queryString("motto")!="" && queryString("motto")!="false"){
            document.write ("<h3>Motto</h3>");
            document.write (decode(queryString("motto")));
        }
        if(queryString("mottotranslated")!="" && queryString("mottotranslated")!="false"){
            document.write ("<h3>Motto Translated</h3>");
            document.write (decode(queryString("mottotranslated")));
        }

        if(queryString("crest")!="" && queryString("crest")!="false"){
            document.write ("<h3>Crest</h3>");
            document.write (decode(queryString("crest")));
        }
        if(queryString("coa")!="" && queryString("coa")!="false"){
            document.write ("<h3>Coat of Arms</h3>");
            document.write (decode(queryString("coa")));
        }
    }
}

它应该重新加载页面并显示新的原点，但我收到此错误，但不幸的是它没有给出代码行。

详细错误是否有帮助？

Uncaught TypeError: Cannot read property 'origin' of null
at HTMLSelectElement.onchange (search-results?surname=Smith&origin=DU&wordorigin=Dutch&hisdata=Spelling+variations+of+this+family+name+include%3A+Smit%2C+Smitt%2C+Smitte%2C+Smites%2C+Smitts%2C+Smiit%2C+Smiites%2C+Smittes%2C+van+Smit%2C+Smut%2C+Smutts%2C+van+Smutts%2C+Schmit%2C+Schmidt%2C+van+Schmidt+and+many+more.+First+found+in+Holland%2C+where+the+name+became+noted+for+its+many+branches+in+the+region%2C+each+house+acquiring+a+status+and+influence+which+was+envied+by+the+princes+of+the+region.+Some+of+the+first+settlers+of+this+family+name+or+some+of+its+variants+were%3A+Claes+Claesen+Smitt%2C+who+arrived+in++New+York%2C+NY+in+1653%3B+Andries+Smit%2C+who+arrived+in++England+or+America+in+1709%3B+Adam+Schmit%2C+who+arrived+in++England+or+America+in+1709.&motto=&mottoTranslated=&crest=Description+not+available&coa=Blue+with+three+gold+horseshoes.+Two+on+top+and+one+below.&numoforigins=5&origin1=DU&originword1=Dutch&origin2=EN&originword2=English&origin3=GR&originword3=German&origin4=IR&originword4=Irish&origin5=SC&originword5=Scottish:302)

有人可以帮忙吗？