I think if the key range from the cnf coming in already contained the null byte, you wouldn't need any special logic for variable length key slots. The ByteUtil.nextKey() would do the right thing in both the fixed length and the null byte terminated case. The seek next hint just has to be bigger than the current row and it'll skip past everything up to the next row that's at or after the key you give it.

The only time you need special logic is for the partial key case, where you need to use the row key passed in here to help form the seek next key. I'm not sure if you're handling that case yet, though.