NULL feilds and ERROR messages from libpq++

I am using the libpq++ interface to interact with a table that has
some NULL fields in it. Why is it that every time I do a
PgDatabase::GetValue on a field that has a NULL value, I get an error
message printed to my console ("PQgetvalue: ERROR! tuple number 0 is
out of range 0..-1")? Is this the normal behavior? It seems very odd
that it would be, since it is common to interact with tables that
contain NULL fields.

Thank You,

Tabor Kelly