I do NestedJoin with FullOuter option, using let's say ID field. There is no ID in right table which do not exists in the left table.
If I filter the result table by other field FOR NULL values, I start to see a row with all the nulls in the table. In other words, it seems like it would be a row in right table which contains ID which doesn't exists in the left table (but it's defenitely not the case). If I filter FOR NOT NULL the same column, null row doesn't appear.
If I change JUST the join to LeftOuter, the null row disappear, so the problem defenitely relates to using FullOuter. There is a number of steps between the join and the filter steps.
For me it seems like an error. I do not have any idea how laziness may influence such a behavior. The null row appeare regardless of existing of ID column at the moment of filtering.