problem with copy_expert on cursor

What would cause the following error when I call copy_expert on a
DictCursor?

SystemError: 'null argument to internal routine'

The sql I pass in is the copy, in a string. The file is a
cStringIO.StringO object. I am using a custom row factory on the
DictCursor. So there are a number of things that could be the source of
the error. However, I am not familiar enough with psycopg to dig this
out.

Incidently, the problem is actually when I am using skytools for
replication, and not actually in any code I have written. I am using
psycopg2 2.3.2. Thanks.

-eric

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