Null values in filters and api.find/stream/findLookupTableValues

Since Cuba Libre 3.4:

• api.find – Rewrites Filter.equal("field", null) to Filter.isNull("field")

• api.stream – Rewrites Filter.equal("field", null) to Filter.isNull("field")

• api.findLookupTableValues – Does not rewrite Filter.equal("field", null) to Filter.isNull("field"), i.e. the filter creates an always false statement and the database always returns no values for such filter.