Negative control Gibson

Hi,

I pcrd fragment 1 (one type of plasmid) and pcrd fragment 2 (another type of plasmid), now o want to assemble them by Gibson.

In the -ve control reactions, I want to include both fragments individually as negative controls, how could I do that pls?

What are other things I should think about for controls?

For the assembly I use neb Gibson mmix

Positive control is neb Gibson positive control fragments

Thanks