DTL Compile Error In Management Portal Not in Studio

I have a requirement which comes down to evaluating two fields, if they are both empty then provide a default value.

If one is empty but the other has a value, then set the empty one to the field with a value.

The screenshots are not the actual fields, I was just using the dtl and fields to prove out the solution.

When I saved and compiled in the Management Portal I got an error, but it still compiled.

I then went to studio and opened the dtl, using view-->other code then compiled and did not get the error.

Wondering if this is a true error or just an anomaly?

The code does at least through the testing tool, perform as desired.

Thanks,