stringbank allows you to hold large numbers of strings without bothering the garbage collector. For small strings storage is reduced as the lengths are encoded compactly.
bits.Len returns 0 when len == 0. That results in a zero result returned by
spaceForLength due to integer division (6/7). The writeLength function is then called using 1 byte to write the zero length value leading to a discrepancy between reserved (0) and written (1) number of bytes.
This causes incorrect values to be returned for empty strings in Stringbank.Get.