ubuntu-defaults-builder doesn't build and doesn't generate depends/recommends in Ubuntu 18.04 and newer

The package fails to build in bionic, artful and newer, as far as I can tell because dh_ubuntu_defaults uses deprecated perl features:

Unescaped left brace in regex is illegal here in regex; marked by <-- HERE in m/\${ <-- HERE distro_release_name}/ at /home/ubuntu/Desktop/ubuntu-defaults-builder-0.57/bin/dh_ubuntu_defaults line 100, <F> line 1.
debian/rules:7: recipe for target 'override_dh_install' failed
make[4]: *** [override_dh_install] Error 255

I've patched bin/dh_ubuntu_defaults by enclosing left brace of ${$var} within square brackets:

--- /usr/bin/dh_ubuntu_defaults 2017-06-23 03:33:59.000000000 +0000
+++ bin/dh_ubuntu_defaults 2020-07-05 04:25:29.909974148 +0000
@@ -97,7 +97,7 @@
  while (/\$\{(\w+)\}/) {
      my $var = $1;
      error "unknown macro: $var" unless exists $macros{$var};
- s/\${$var}/$macros{$var}/g;
+ s/\$[{]$var}/$macros{$var}/g;
  }

  push @lines, $_;

Now tests doesn't fail, but when I build defaults package dh_ubuntu_defaults doesn't generate depends/recommends in Ubuntu 18.04 and newer if there is a folder "ubiquity-slideshow" in defaults package - I get warnings during build of my ubuntu-defaults package:

dh_install
dh_ubuntu_defaults --disable-restrictions
dh_ubuntu_defaults: doit() + doit_*() calls will no longer spawn a shell in compat 12 for single string arguments (please use complex_doit instead)
dh_ubuntu_defaults: This feature will be removed in compat 12.
dh_ubuntu_defaults: doit() + doit_*() calls will no longer spawn a shell in compat 12 for single string arguments (please use complex_doit instead)
dh_ubuntu_defaults: This feature will be removed in compat 12.
dh_ubuntu_defaults: doit() + doit_*() calls will no longer spawn a shell in compat 12 for single string arguments (please use complex_doit instead)
dh_ubuntu_defaults: This feature will be removed in compat 12.
make[1]: Leaving directory '/home/ubuntu/Desktop/ubuntu-defaults-baltix-master'
   dh_installdocs
   dh_installchangelogs
   dh_installgsettings
   dh_icons
   dh_perl
   dh_configpackage
   dh_link
   dh_strip_nondeterminism
   dh_compress
   dh_fixperms
   dh_missing
   dh_installdeb
   dh_gencontrol
dpkg-gencontrol: warning: Depends field of package ubuntu-defaults-baltix: unknown substitution variable ${ubuntudefaults:Depends}
dpkg-gencontrol: warning: Recommends field of package ubuntu-defaults-baltix: unknown substitution variable ${ubuntudefaults:Recommends}

I'd rather someone who knew perl better than me take a look at this.