I have a Moose class with an attribute that is not required. When I try to access this attribute in an object where it is not present, the warning message "Use of uninitialized value in concatenation (.) or string" is generated. How can I check for the presence of an optional attribute without generating the warning message?

The sample code below is a simple Moose class with 1 required attribute (name) and 1 optional attribute (age). The 'show_person' method generates the warning message because $self->age() is not present in the current object.

Just referencing $self->age() in 'show_person' to test it generates the warning, as in:
if ($self->age() ne '') {...};

#!/usr/bin/perl

package Person;
use Moose;

has 'name' => ( is  => 'ro', isa => 'Str', required => 1);
has 'age'  => ( is  => 'ro', isa => 'Str');

sub show_person {
   my $self = shift;
   return $self->name() . " " . $self->age();
}

__PACKAGE__->meta->make_immutable;
no Moose;
1;

my $person = Person->new(name => "Bob");
print "\n", $person->show_person(), "\n";
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