If a hashFn returns an odd length string, the buffer removes the last digit

[Matan-Fridman]

My hash fn sometimes returns odd length strings and returns them as the hash of two leaves. Then behind the scenes this string probably gets turned to a buffer before it gets sent to the fn again. The problem is that a buffer from a hex string needs to be even in order to remain untouched. If its odd length it will remove the last digit. Is there a solution?