Dpkg::Source::Package: Do not assume $ENV{'HOME'} is defined

Closes: #677631

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Guillem Jover <guillem@debian.org>

debian/changelog

@@ -23,6 +23,8 @@ dpkg (1.16.5) UNRELEASED; urgency=low
     different version from the source package. Closes: #440094, #672723
   * Minimize source architecture list on «dpkg-source -b» by removing
     architectures already covered by architecture wildcards. Closes: #675333
+  * Do not assume $ENV{'HOME'} is defined in Dpkg::Source::Package.
+    Thanks to Niels Thykier <niels@thykier.net>. Closes: #677631
 
   [ Updated dpkg translations ]
   * Swedish (Peter Krefting).

scripts/Dpkg/Source/Package.pm

@@ -349,7 +349,7 @@ sub check_signature {
         push @exec, "gpg", "--no-default-keyring", "-q", "--verify";
     }
     if (scalar(@exec)) {
-        if (-r "$ENV{'HOME'}/.gnupg/trustedkeys.gpg") {
+        if (defined $ENV{'HOME'} and -r "$ENV{'HOME'}/.gnupg/trustedkeys.gpg") {
             push @exec, "--keyring", "$ENV{'HOME'}/.gnupg/trustedkeys.gpg";
         }
         foreach my $vendor_keyring (run_vendor_hook('keyrings')) {