Query of $ne null not working

[Kenner Stross]

I am trying to query for a field not being null, yet the query being passed doesn't appear to be constructed properly.  The relevant line of code that constructs the query (which is part of an aggregate pipeline) is:

BSONDocument("$match" -> BSONDocument("pf.ps" -> BSONDocument("$ne" -> null)))

... but the resulting section of the query looks like:

{ pf.ps: {} } }

Bug?  Or should I be constructing this in some other manner?

Thanks,

Kenner

[Marcel Snijkers]

BSONDocument("$ne" -> BSONNull) works for me.