WCF Socket Connection aborted due to DBNull

I've been delving a fair bit into WCF lately and have been encountering enough gotchas that it is clear that it's time for me to resurrect my tech blog.  My first post: an errant WCF Socket Exception which looks like a timeout due to the message is actually an exception caused by DBNull.

You may have come across the above msg at some point in working with WCF.

The socket connection was aborted. This could be caused by an error processing your message or a receive timeout being exceeded by the remote host, or an underlying network resource issue. Local socket timeout was '00:00:30'.

Oddly however, none of my binding config settings actually set a timeout of 30 seconds and even more oddly, the message appears almost instantly.

After a tremendous amount of hassle, it was only through some testing that I discovered that a database query in my data access service was returning an unexpected DBNull for a function which when called by my client caused it to abort the socket connection without giving me any details as to why.  On the service side it looked like everything was perfect while the client side blew up with what looked like a timeout.

Moral of the story?  If you get something that looks like a timeout, check the data source first.