APEX 4.1 Shuttle Null on Right - oracle-apex

Question

APEX version: 4.1.1.00.23
I have a shuttle that populates the right site based on what is chosen from a select list. Whenever an item is picked from the select list, the correct item or items are populated on the right panel, but there is always a null that is added. How do I get ride of the null?
Shuttle name: P51_Shuttle
Select list name: P51_Analyst
Here is my code:
HTML Header:
<script type="text/javascript">
function LoadRightPane()
{
var objDQAnalyst = document.getElementById("P51_DQ_ANALYST");
var ajaxRequest = new htmldb_Get(null,&APP_ID.,'APPLICATION_PROCESS=get_DQAttributes',0);
ajaxRequest.add('P51_DQ_ANALYST',objDQAnalyst.value);
ajaxResult = ajaxRequest.get();
//alert(ajaxResult);
if(ajaxResult)
{
var shuttleRight = document.getElementById("P51_SHUTTLE_RIGHT");
shuttleRight.options.length = 0;
var attrArray = ajaxResult.split("~colsep~");
for(var i=0; i < attrArray.length; i++) {
shuttleRight.options[i] = new Option(attrArray[i], attrArray[i]);
}
}
else
{
shuttleRight.options.length = 0;
}
ajaxRequest = null;
}
function moveitem(item) {
return;
s_left = document.getElementById("P51_SHUTTLE_TO_LEFT");
db.transaction(function(tx){
tx.executeSql('select distinct DQ_ATTRIBUTE from DQ_MANUAL_EDIT where DQ_ANALYST = ?',[item],function(tx,results)
{
for (var i=0; i < s_left.options.length;i++)
{
if (results.value == s_left.options[i].value)
{
s_left.options[i].selected = true;
g_Shuttlep_v15.move();
}
}
});
});
}
</script>
Page HTML Body Attribute:
onLoad="Javascript:LoadRightPane();"
Applicaiton/Page process called (get_DQAttributes)
DECLARE
L_RETURN VARCHAR2(2000):= NULL ;
BEGIN
BEGIN
FOR rec IN (
select distinct dq_attribute
from DQ_MANUAL_EDIT
where dq_analyst = :P51_DQ_ANALYST
)
LOOP
L_RETURN := L_RETURN || rec.dq_attribute || '~colsep~' ;
END LOOP;
end;
htp.prn(L_RETURN);
END;

Answer 1

Your ajax process always returns something suffixed with ~colsep~
When you run a string like that in firebug:
"test1~colsep~".split("~colsep~")
The result will be an array with 2 elements:
["test1", ""]
So your NULL element originates from that. To fix this just adjust the ajax process to trim the last separator with RTRIM.
DECLARE
L_RETURN VARCHAR2(2000):= NULL ;
BEGIN
FOR rec IN ( select distinct dq_attribute
from DQ_MANUAL_EDIT
where dq_analyst = :P51_DQ_ANALYST)
LOOP
L_RETURN := L_RETURN || rec.dq_attribute || '~colsep~' ;
END LOOP;
l_return := rtrim(l_return, '~colsep~');
htp.prn(L_RETURN);
END;

Answer 2

Everything about Tom's answer is correct. I had to make one modification to the line
l_return := rtrim(l_return, '~colsep~');
When running that code, the last two letters would be removed. And if I had multiple items in the shuttle, the first item would be fine, but the second one would be cut off.
For example:
Using the code: l_return := rtrim(l_return, '~colsep~');
the right panel of the shuttle would look like this
Score
Da
But the actual text should be
Score
Data
So I used the 'substr' function and now it is working
l_return := substr(l_return,0,(length(l_return)-8));
Here is the whole code
DECLARE
L_RETURN VARCHAR2(2000):= NULL ;
BEGIN
FOR rec IN ( select distinct dq_attribute
from DQ_MANUAL_EDIT
where dq_analyst = :P51_DQ_ANALYST)
LOOP
L_RETURN := L_RETURN || rec.dq_attribute || '~colsep~' ;
END LOOP;
L_RETURN := substr(l_return,0,(length(l_return)-8));
htp.prn(L_RETURN);
END;
Thank you Tom for getting my mental ball rolling!!!