"zero values" = no value at all, nothing (not a 0, not a NULL, not a "" ... just nothing)
OBIEE will never generate data which doesn't exist, so you better fix that during ETL to add at least an empty/NULL/zero row at that point.
Or you need to model things to cover this case with the right logic (or use EVALUATE to send a LAG call to the DB and try it in that way ....)
+1 to Gianni
"zero values", NULL, '', 0 are completely different things and technically, logically and mathematically not to be used interchangeably!