Copy Package with null as source

Hi,

I am on bpc 10 nw.

I have source data of [2010.Jan, 2010.Feb, 2010.Mar] = [null, 1,2] in Category = Actual.

And target data of [2010.Jan, 2010.Feb, 2010.Mar] = [100, 200, 300] in Category = Budget.

With the standard copy package,

if i copy from

[2010.Jan, 2010.Feb, 2010.Mar] in Actual -->

[2010.Jan, 2010.Feb, 2010.Mar] in Budget,

the end result becomes

[2010.Jan, 2010.Feb, 2010.Mar] = [0, 1, 2] in Category = Budget.

What parameter can i change in 'Modify Script' or 'Process Chain', such that source = null is ignored, while source = 0 is used?

So instead of the results becoming

[2010.Jan, 2010.Feb, 2010.Mar] = [0, 1, 2] in Category = Budget,

i want the results to be

[2010.Jan, 2010.Feb, 2010.Mar] = [100, 1, 2] in Category = Budget.

Thanks,

LC