Another Conditional Formatting Question

Hi, I understand you can't hijack another thread so I'm starting this separate one. I have a backlog template into which I post a daily order backlog that I extract from and Oracle Discoverer report. Some order have shipping sets, others do not, depending on whether the customer will accept partial shipments. The default entry from an order with no ship set is NULL.

I'm trying to set a conditional format whereby any cell that doesn't contain NULL (i.e has a ship set) will be formatted red to highlight this to my order release team.

I tried using "use a formula to determine which cells to format," and set the rule as =$C$1<>"NULL" but that isn't working. The column format is general, and I've also tried setting the format as text.

This is about the extent of my knowledge here - help!

Thanks.