sub maybe_set_param {
  my ( $self, $param, $default, $value ) = @_;
  $self->session->param( $param => defined $value ? $value : $default );
}

##</code><code>##

$self->maybe_set_param( page => $post{ page }, 1 );

##</code><code>##

sub maybe_set_param {
  my ( $self, $param, $default ) = @_;
  my $value = $self->post->{ $param };
  $self->session->param( $param => defined $value ? $value : $default );
}
# ...
$self->maybe_set_param( page => 1 );

##</code><code>##

sub maybe_set_param {
  my $self     = shift;
  my %defaults = @_;
  my $post     = $self->post;
  while ( my ( $param, $default ) = each %defaults ) {
    my $value = $post->{ $param };
    $self->session->param( $param => defined $value ? $value : $default );
  }
}

##</code><code>##

$self->maybe_set_param( page => 1, foo => 15, bar => -1 );