If this EXEC parameter is specified, the unload utilities unload null values as zeroes. The parameter setting OLDNULL=Y allows for compatibility with earlier TIBCO Object Service Broker releases and for tables being unloaded but not intended for reloading.
You cannot represent a floating point null in fixed format. When a floating point null is unloaded using S6BBRULB or S6BBRULH, it is unloaded as true zero. Therefore, when floating point nulls are reloaded using S6BBRTBL, they are loaded as a zero.