A practical fix in CS5 is to sample the existing sky and stretch it into the gap, then blend it.

One community solution was:

1. Select a very thin strip or single row of pixels from a nearby clean area of sky.
2. Stretch/transform that strip to cover the empty area up to the frame edges.
3. Use the Spot Healing Brush a few times to break up banding or stretching artifacts and help the fill blend in.

This works better than Content-Aware Fill when the missing area sits close to buildings or other edges, because Content-Aware may pull in unwanted detail. A plain gradient often looks artificial if the sky already has subtle horizontal variation, while stretching real sky pixels preserves the original color and tone better.

If needed, sample from a part of the sky closest in brightness to the gap for the most natural match.