Posting A Value For A Field In Select Option

I have an ASP admin script where I'm adding records, and I have a
category that already has set name values hard-coded into a selct option
pulldown, but if the user wants to create a new category and not use the
select pulldown, the value will end up being " , newvalue" when posting
from this sequence of pulldown and input text box:

<select name="CategoryName">
<option selected></option>
<option value="first">first category</option>
<option value="second">second category</option>
</select>
<br>
New Category<br>
<input name="CategoryName" type="text" size="26"
maxlength="255">

What is the best way of not having that extra preceeding comma appear as
the value if the user chooses to add a brand new category?