diff -up ./lib/HTML/TreeBuilder/LibXML/Node.pm.orig ./lib/HTML/TreeBuilder/LibXML/Node.pm
--- ./lib/HTML/TreeBuilder/LibXML/Node.pm.orig	2021-06-14 17:00:06.781971373 +0200
+++ ./lib/HTML/TreeBuilder/LibXML/Node.pm	2021-06-14 17:02:22.456482166 +0200
@@ -74,7 +74,8 @@ sub as_HTML {
     {
         local $@; # protect existing $@
         my $output = eval { $_[0]->{node}->toStringC14N(1) };
-        return $@ ? $_[0]->{node}->toString : $output;
+        return $_[0]->{node}->toString if ($@ or $output eq '');
+        return $output;
     }
 }
 
diff -up ./t/05_empty.t.orig ./t/05_empty.t