The documentation lists this format for using bind values:

$rv  = $dbh->do($statement, \%attr, @bind_values);
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I am surprised that your snippet even compiles or passes the SQL parser, but in any case, I don't think that you are doing what you think you are doing.

To expand on the synopsis example, do:

my $statement   = q{INSERT INTO....};
my %attr        = ();
my @bind_values = ( 'NULL', $first, $last );

my $rv = $dbh->do( $statement, \%attr, @bind_values );
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and see what happens.