DBD::Pg's $dbh->func( "/path/to/file", 'lo_import' ) fails silently

I'm trying to use Perl's DBD::Pg module to import a file as a large object.
For this I'm using the following:
my $oid = $dbh->func( "/absolute/path/to/file", 'lo_import' );

When I do this, a new record is added to pg_largeobject, with a
proper-looking non-null loid, but the data field remains empty, and the
variable $oid above gets a return value of undef, i.e. the call to func
fails. No error warning is ever emitted, as far as I can tell. ($dbh->errstr
returns undef.) FWIW, the file passed as the first argument is
world-readable, and the full path to it is world-accessible.

I've read the documentation for Perl's DBI and DBD::Pg modules, but I can't
find any information that will enable me to troubleshoot/debug this further.
Any suggestions would be greatly appreciated!

TIA!

Kynn