Good advice from Colin and Larry. I have done both at different projects with very good result.
On my workbench I did as Colin said and filled the void with sawdust. Really packed it in there. Then I used CA glue (thin superglue) to soak the sawdust. After it set I sanded the area flush. It has been holding up good so far.
I would guess this way might not work so well if the sap pocket is very big/wide as it could feel “hard” compared to the wood surface and maybe crack if hit with a pointy object, depending on how deep the sawdust was soaked with superglue that is.