Problem requesting results using 'NULL' where condition in /IWFND/GW_CLIENT

I have a CDS view which is exposed via SADL framework to a GW service.

The CDS view contains a propertie called workOrderWorkCentreId with the following technical details:

Using the GW_CLIENT transaction, when I try to obtain the result set from the entity (= CDS result set) with the condition workOrderWorkCentreId eq 'NULL' no records are displayed. Which is wrong, since the CDS contains records where this field is empty.

GW_CLIENT request:

Did a trace with ST05 to evaluate the SQL request and found this:

Detailed view:

It seems like the SADL framework is building the SQL request considering the field length size in the where condition.

Since the property workOrderWorkCentreId maximum length size is 2 characters, it is truncating the NULL condition to 'nu' resulting in the wrong result set.

I did a quick test with other properties with largest length size and it worked fine.

Any ideas on how to overcome this problem?

Cheers.