I am fairly new to mapping XML into an excel spreadsheet, and I need some
help to make the spreadsheet behave the way I want.

I receive an xml file from an outside application that is in this format:

<?xml version"1.0"?
<Master
<Header
<HeaderInfo...</HeaderInfo
</Header
<Record
<Reference type="A"a1</Reference
<Reference type="B"b1</Reference
</Record
<Record
<Reference type="A"a2</Reference
</Record
<Record
<Reference type="A"a3</Reference
<Reference type="B"b3</Reference
</Record
</Master

Basically, there isn't always a Reference Type "B". I want to map these
into excel into two columns, like:

a1 b1
a2
a3 b3

What I did is set up two source maps, mapped one using type="A" into one
column, and type="B" into the other. Unfortunately, I get this:

a1 b1
a2 b3
a3

Is there a way to have the map pull a blank if there is no Type B entry,
instead of skipping over it? This is probably pretty rudimentary, but I
can't figure it out.
Thanks in advance for your help.