ncurses: Cleanup abi version

pkgs/development/libraries/ncurses/default.nix

@@ -4,8 +4,8 @@
 , gpm ? null
 
 # Extra Options
+, abiVersion ? "5"
 , unicode ? true
-, abiVersion ? null
 }:
 
 let
@@ -35,6 +35,7 @@ stdenv.mkDerivation rec {
   buildInputs = [ optGpm ];
 
   configureFlags = [
+    (mkWith   true        "abi-version" abiVersion)
     (mkWith   true        "cxx"         null)
     (mkWith   true        "cxx-binding" null)
     (mkWith   false       "ada"         null)
@@ -56,7 +57,7 @@ stdenv.mkDerivation rec {
     (mkEnable unicode     "widec"       null)
     (mkEnable true        "ext-colors"  null)
     (mkEnable true        "ext-mouse"   null)
-  ] ++ stdenv.lib.optional (abiVersion != null) (mkWith true "abi-version" abiVersion);
+  ];
 
   # PKG_CONFIG_LIBDIR is where the *.pc files will be installed. If this
   # directory doesn't exist, the configure script will disable installation of