As you can see from line 802

while ( my $ref = $self->fetch_assoc($sth) )
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the method fetch_assoc() expects a statement handler. The usual way to do it would be:

my $dbh = DBI->connect(@db_args);
my $sql = "SELECT email FROM database.table";
my $sth = $dbh->prepare($sql);
$sth->execute();
while (my $hashref = $sth->fetchrow_hashref) {
    ...
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But obviously your module is intervening, so you need to find how to acquire the statement handler $sth from the module - possibly:

my $sth = $db->query($sql)...
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Also you need to work out what type of data structure fetch_assoc() is returning - I don't think it's returning an array (@row) as you expect in your code, more likely a hash reference, use Data::Dumper to find out.