Young tree - small cavity - what to do?

Hi I've got an apple tree planted in January - I'm growing it espaliered on the garden wall.
I went to lower the first tier branches to horizontal today and while I was there noticed a small cavity in the centre of the pruning cut that I made on the central leader back then.
its small - only 1-2mm diameter - but I could see water in it.
Do I need to do anything about this or is it best left alone? Like cutting a shallow channel for the water to drain out? If so should I do this now or wait until late winter/early spring?

Old photo but it shows the cut - pre cavity
I went to lower the first tier branches to horizontal today and while I was there noticed a small cavity in the centre of the pruning cut that I made on the central leader back then.
its small - only 1-2mm diameter - but I could see water in it.
Do I need to do anything about this or is it best left alone? Like cutting a shallow channel for the water to drain out? If so should I do this now or wait until late winter/early spring?

Old photo but it shows the cut - pre cavity
East Yorkshire
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Posts
If you look at this drawing of a tree branch cross section
https://treegrowthstructure.weebly.com/cross-section-of-a-tree.html
you’ll see that the little hole you have spotted is the pith. The pith is surrounded by essentially dead wood. The tree doesn’t need the dead wood for anything other than support. All the activity in the tree goes on in the outer layers.
If you start cutting channels you’ll be messing about with the living tissue, which really will invite trouble.
If you live in Derbyshire, as I do.