Dear Maintainer,

debtree fails with this error for a number of packages:
  Can't use string ("") as a HASH ref while "strict refs" in use at /usr/bin/debtree line 329.

Example test case:
  debtree gcc-12-multilib:amd64

The root cause appears to lie within an unhandled third condition in
  sub get_apt_pinfo {}

If the $pdata exists, but does neither meet the if ($show_installed ...), nor the elsif (exists $$pdata ...), then the sub is returning
something that is interpreted as an "". The behaviour changes when a final/closing empty else {} branch is added.

Note: This effect was also seen on KUbuntu 24.04 for
        debtree gcc-13-x86-64-linux-gnu:amd64
Note: This bug may be related to
        bug report #954795



Adding the empty else {} changes the error to
  Use of uninitialized value in string eq at /usr/bin/debtree line 329.

The root cause for this appears to be within the
  check_version {}
which doesn't check, if $$pinfo{VerStr} actually exists before trying to eq it with $version.

Adding a check like this
  sub check_version {
    my ($package, $version) = @_;
      my $pinfo = get_apt_pinfo($package, "");
    if (exists ${$pinfo}{VerStr}) {
      return ($$pinfo{VerStr} eq $version);
    } else {
      return 0;
    }
  }
seems to remove the error.

Note: This "uninitialized value" error can be reproduced directly on KUbuntu 24.04 by issuing
        debtree g++-13-x86-64-linux-gnu:amd64


The HASH error stops debtree from creating a viable .gv file, as it seems to stop in the middle of the process.
The corruption prevents any rendering.
This may be related to
  bug report #1003856



I am not a Perl developer, but tried to make a best effort to try to narrow down the root cause.
I hope this helps finding and fixing the issue.


Best regards,
Renzo de Paoli


Concordia Domi Foris Pax