Can you please describe in more detail what kind of error you are getting. I have tried the following code, which gave exactly the behaviour you wanted. So I suspect the problem could be with the values of your $uri and $proxy. Perhaps they are empty. You could insert a print statement before your object creation and check the value of $uri and $proxy. The following code is what I used to test your object creation, which worked perfectly.

use strict;
use SOAP::Lite;
use Data::Dumper;

my $uri = "Optional URI";
my $proxy = "HTTPS:";

# <== insert print statement here to inspect $uri and $proxy
print "URI = [$uri], PROXY = [$proxy]\n";

my $soap = SOAP::Lite->new(
  uri => ($uri || 'Some URI'),
  proxy => ($proxy || 'HTTP:')
  );

print Dumper($soap);
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