dpkg-buildflags: error out when a required parameter is missing

debian/changelog

@@ -10,6 +10,8 @@ dpkg (1.15.7.2) UNRELEASED; urgency=low
     Closes: #579724
     Document this behaviour in the API and add non-regression test to ensure
     it's kept.
+  * Let dpkg-buildflags error out when a required parameter is missing.
+    Closes: #579722
 
   [ Guillem Jover ]
   * Add powerpcspe support to ostable and triplettable.

scripts/dpkg-buildflags.pl

@@ -62,6 +62,7 @@ while (@ARGV) {
             if defined($action);
         $action = $1;
         $param = shift(@ARGV);
+	usageerr(_g("%s needs a parameter"), $_) unless defined $param;
     } elsif (m/^--list$/) {
         usageerr(_g("two commands specified: --%s and --%s"), "list", $action)
             if defined($action);