If you want to use a namespace prefix, you have to register it first: 
#!/usr/bin/perl
use warnings;
use strict;

use XML::LibXML;

my $xml = XML::LibXML->load_xml( location => '1.xml');
my $xpc = XML::LibXML::XPathContext->new($xml);
$xpc->registerNs('contact', 'urn:ietf:params:xml:ns:contact-1.0');
for my $name (qw(rem add)) {
    for my $node ($xpc->findnodes("//contact:$name".'[not(*|text()|@*|
+processing-instruction()|comment())]', $xml->documentElement)) {
        $node = $node->parentNode->removeChild($node);
    }
}
print $xml->serialize;

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لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: How to remove empty XML elements using XML::LibXML by choroba
in thread How to remove empty XML elements using XML::LibXML by FreakyGreenLeaky

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