--- mysql-server-5.7.postinst.orig      2016-07-20 16:07:54.588204593 +0000
+++ mysql-server-5.7.postinst   2016-07-20 16:08:30.616393444 +0000
@@ -169,7 +169,7 @@
     db_set mysql-server/postrm_remove_database false || true
 
     # Fix old options that were deprecated in 5.5 and removed in 5.7
-    if dpkg --compare-versions "$2" le-nl "5.7.13-0ubuntu0~"; then
+    if [ "$2" = "" ] || dpkg --compare-versions "$2" le-nl "5.7.13-0ubuntu0~"; then
       echo "Renaming removed key_buffer and myisam-recover options (if present)"
       fix_old_config_options
     fi