dpkg-source: internal error "Use of uninitialized value ..."

Binary package hint: dpkg

dpkg-source fails in the "empty-diff" test of lintian and lets the package fail to build (bug #742092).

You can reproduce it by getting the source of lintian and run:

$ debian/rules runtests onlyrun=cruft-empty-diff
.... running tests ....
rm -rf debian/tests
mkdir debian/tests
private/runtests -j 4 cruft-empty-diff
Package tests:
Running cruft-empty-diff 1.0-1... building... testing... FAILED:
--- t/tests/cruft-empty-diff/tags 2011-03-22 23:06:53.716331766 +0100
+++ debian/tests/cruft-empty-diff/tags.cruft-empty-diff 2011-03-24 15:01:00.637531630 +0100
@@ -1 +1,7 @@
-W: cruft-empty-diff source: empty-debian-diff
+Use of uninitialized value $file in -e at /usr/share/perl5/Dpkg/Source/Functions.pm line 77.
+Use of uninitialized value $file in open at /usr/share/perl5/Dpkg/Source/Functions.pm line 78.
+dpkg-source: error: cannot write %s: No such file or directory
+internal error: dpkg-source -x failed with status
+internal error: 2
+warning: collect info unpacked about package cruft-empty-diff failed
+warning: skipping check of source package cruft-empty-diff
make: *** [runtests] Fehler 1

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: dpkg 1.16.0~ubuntu5
ProcVersionSignature: Ubuntu 2.6.38-7.38-generic 2.6.38
Uname: Linux 2.6.38-7-generic x86_64
Architecture: amd64
Date: Thu Mar 24 23:49:28 2011
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Alpha amd64 (20100921.1)
ProcEnviron:
 LANGUAGE=de_DE:en
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: dpkg
UpgradeStatus: Upgraded to natty on 2011-03-11 (13 days ago)