Fix postinst broken in 9.0.0~exp2 on install (and not upgrade) of the package.

debian/changelog

@@ -3,8 +3,10 @@ desktop-base (9.0.0) UNRELEASED; urgency=medium
   [ Aurélien COUDERC ]
   * Implement Plymouth splash for Stretch’s soft Waves theme.
     (Closes: #843998, #842078)
-  *  Prepare for plymouth splash integration into theme packs that will allow
-     splash selection via alternatives in the future.
+  * Prepare for plymouth splash integration into theme packs that will allow
+    splash selection via alternatives in the future.
+  * Fix postinst broken in 9.0.0~exp2 on install (and not upgrade) of the
+    package.
 
  -- Aurélien COUDERC <zecoucou@free.fr>  Tue, 27 Dec 2016 17:58:13 +0100
 

debian/postinst

@@ -4,7 +4,7 @@ set -e
 # Tag to allow some debhelper commands to inject relevant code
 #DEBHELPER#
 
-if [ "${1}" = "configure" ]; then
+if [ "${1}" = "configure" ] && [ ! -z "${2}" ]; then
     if dpkg --compare-versions ${2} le "9.0.0~exp1"; then
         # Try remove folder if empty, left after 9.0.0~exp1 conf suppression
         # by debhelper conffile handling