* "!isNull x" -> "x != null". Done automatically. Hope nothing

  broke.

svn path=/nixpkgs/trunk/; revision=870

47 files changed, 81 insertions, 81 deletions

diff --git a/pkgs/applications/graphics/gqview/default.nix b/pkgs/applications/graphics/gqview/default.nix
index b507c67b5f53..2fd40e983b60 100644
--- a/pkgs/applications/graphics/gqview/default.nix
+++ b/pkgs/applications/graphics/gqview/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, pkgconfig, gtk, libpng}:
 
-assert !isNull pkgconfig && !isNull gtk && !isNull libpng;
+assert pkgconfig != null && gtk != null && libpng != null;
 # Note that we cannot just copy gtk's png attribute, since gtk might
 # not be linked against png.
 assert libpng == gtk.libpng;
diff --git a/pkgs/applications/networking/browsers/firefox/default.nix b/pkgs/applications/networking/browsers/firefox/default.nix
index 9c7a434c63b4..aaee20e74814 100644
--- a/pkgs/applications/networking/browsers/firefox/default.nix
+++ b/pkgs/applications/networking/browsers/firefox/default.nix
@@ -1,8 +1,8 @@
 { stdenv, fetchurl, pkgconfig, gtk, perl, zip, libIDL
 }:
 
-assert !isNull pkgconfig && !isNull gtk && !isNull perl
-  && !isNull zip && !isNull libIDL;
+assert pkgconfig != null && gtk != null && perl != null
+  && zip != null && libIDL != null;
 
 assert libIDL.glib == gtk.glib;
 
diff --git a/pkgs/applications/video/MPlayer/default.nix b/pkgs/applications/video/MPlayer/default.nix
index d2b089bbb85f..a064162d8804 100644
--- a/pkgs/applications/video/MPlayer/default.nix
+++ b/pkgs/applications/video/MPlayer/default.nix
@@ -1,8 +1,8 @@
 { alsaSupport ? false
 , stdenv, fetchurl, x11, freetype, alsa ? null}:
 
-assert !isNull x11 && !isNull freetype;
-assert alsaSupport -> !isNull alsa;
+assert x11 != null && freetype != null;
+assert alsaSupport -> alsa != null;
 
 derivation {
   name = "MPlayer-1.0pre3";
diff --git a/pkgs/applications/video/mplayerplug-in/default.nix b/pkgs/applications/video/mplayerplug-in/default.nix
index c06fc31fee42..5337325e4269 100644
--- a/pkgs/applications/video/mplayerplug-in/default.nix
+++ b/pkgs/applications/video/mplayerplug-in/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, x11}:
 
-assert !isNull x11;
+assert x11 != null;
 
 derivation {
   name = "mplayerplug-in-1.0pre2";
diff --git a/pkgs/applications/video/vlc/default.nix b/pkgs/applications/video/vlc/default.nix
index da48bc7e46c0..3776f5a23844 100644
--- a/pkgs/applications/video/vlc/default.nix
+++ b/pkgs/applications/video/vlc/default.nix
@@ -1,9 +1,9 @@
 { stdenv, fetchurl, x11, wxGTK, libdvdcss, libdvdplay
 , mpeg2dec, a52dec, libmad, alsa}:
 
-assert !isNull x11 && !isNull wxGTK && !isNull libdvdcss
-  && !isNull libdvdplay && !isNull mpeg2dec && !isNull a52dec
-  && !isNull libmad && !isNull alsa;
+assert x11 != null && wxGTK != null && libdvdcss != null
+  && libdvdplay != null && mpeg2dec != null && a52dec != null
+  && libmad != null && alsa != null;
 assert libdvdplay.libdvdread.libdvdcss == libdvdcss;
 
 derivation {
diff --git a/pkgs/applications/video/zapping/default.nix b/pkgs/applications/video/zapping/default.nix
index 613053bd8102..809ca969d801 100644
--- a/pkgs/applications/video/zapping/default.nix
+++ b/pkgs/applications/video/zapping/default.nix
@@ -5,15 +5,15 @@
 , libglade, scrollkeeper, esound, gettext
 , zvbi ? null, libjpeg ? null, libpng ? null }:
 
-assert !isNull pkgconfig && !isNull perl && !isNull python &&
-  !isNull x11 && !isNull libgnomeui && !isNull libglade &&
-  !isNull scrollkeeper && !isNull esound && !isNull gettext;
+assert pkgconfig != null && perl != null && python != null &&
+  x11 != null && libgnomeui != null && libglade != null &&
+  scrollkeeper != null && esound != null && gettext != null;
 
-assert teletextSupport -> !isNull zvbi && zvbi.pngSupport
+assert teletextSupport -> zvbi != null && zvbi.pngSupport
   && pngSupport && zvbi.libpng == libpng;
 
-assert jpegSupport -> !isNull libjpeg;
-assert pngSupport -> !isNull libpng;
+assert jpegSupport -> libjpeg != null;
+assert pngSupport -> libpng != null;
 
 derivation {
   name = "zapping-0.7cvs6";
diff --git a/pkgs/data/sgml+xml/schemas/xml-dtd/docbook/default.nix b/pkgs/data/sgml+xml/schemas/xml-dtd/docbook/default.nix
index befa46fd3681..a27d35d6cc61 100644
--- a/pkgs/data/sgml+xml/schemas/xml-dtd/docbook/default.nix
+++ b/pkgs/data/sgml+xml/schemas/xml-dtd/docbook/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, unzip}:
 
-assert !isNull unzip;
+assert unzip != null;
 
 derivation {
   name = "docbook-xml-4.2";
diff --git a/pkgs/development/libraries/fontconfig/default.nix b/pkgs/development/libraries/fontconfig/default.nix
index 15944697423e..c9340043d90f 100644
--- a/pkgs/development/libraries/fontconfig/default.nix
+++ b/pkgs/development/libraries/fontconfig/default.nix
@@ -1,9 +1,9 @@
 {stdenv, fetchurl, x11, freetype, expat, ed}:
 
-assert !isNull x11 && x11.buildClientLibs;
-assert !isNull freetype;
-assert !isNull expat;
-assert !isNull ed;
+assert x11 != null && x11.buildClientLibs;
+assert freetype != null;
+assert expat != null;
+assert ed != null;
 
 derivation {
   name = "fontconfig-2.2.90";
diff --git a/pkgs/development/libraries/gnet/default.nix b/pkgs/development/libraries/gnet/default.nix
index 0475dfa06ab1..cccf0e0d36c1 100644
--- a/pkgs/development/libraries/gnet/default.nix
+++ b/pkgs/development/libraries/gnet/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, pkgconfig, glib}:
 
-assert !isNull pkgconfig && !isNull glib;
+assert pkgconfig != null && glib != null;
 
 derivation {
   name = "gnet-2.0.4";
diff --git a/pkgs/development/libraries/gnome/GConf/default.nix b/pkgs/development/libraries/gnome/GConf/default.nix
index 0c6f0dfe0105..31f144b1d79d 100644
--- a/pkgs/development/libraries/gnome/GConf/default.nix
+++ b/pkgs/development/libraries/gnome/GConf/default.nix
@@ -1,8 +1,8 @@
 {stdenv, fetchurl, pkgconfig, perl, glib, gtk, libxml2, ORBit2, popt}:
 
-assert !isNull pkgconfig && !isNull perl
-  && !isNull glib && !isNull gtk
-  && !isNull libxml2 && !isNull ORBit2 && !isNull popt;
+assert pkgconfig != null && perl != null
+  && glib != null && gtk != null
+  && libxml2 != null && ORBit2 != null && popt != null;
 
 derivation {
   name = "GConf-2.4.0.1";
diff --git a/pkgs/development/libraries/gnome/ORBit2/default.nix b/pkgs/development/libraries/gnome/ORBit2/default.nix
index 8af6c7fe4ecc..8203db963ca9 100644
--- a/pkgs/development/libraries/gnome/ORBit2/default.nix
+++ b/pkgs/development/libraries/gnome/ORBit2/default.nix
@@ -1,7 +1,7 @@
 {stdenv, fetchurl, pkgconfig, glib, libIDL, popt}:
 
-assert !isNull pkgconfig && !isNull glib && !isNull libIDL
-  && !isNull popt;
+assert pkgconfig != null && glib != null && libIDL != null
+  && popt != null;
 
 derivation {
   name = "ORBit2-2.8.3";
diff --git a/pkgs/development/libraries/gnome/esound/default.nix b/pkgs/development/libraries/gnome/esound/default.nix
index cf70712cd6d5..7e51b9d6fba6 100644
--- a/pkgs/development/libraries/gnome/esound/default.nix
+++ b/pkgs/development/libraries/gnome/esound/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, audiofile}:
 
-assert !isNull audiofile;
+assert audiofile != null;
 
 derivation {
   name = "esound-0.2.32";
diff --git a/pkgs/development/libraries/gnome/gnome-mime-data/default.nix b/pkgs/development/libraries/gnome/gnome-mime-data/default.nix
index 62e32d01e4da..ffcd6d19a78c 100644
--- a/pkgs/development/libraries/gnome/gnome-mime-data/default.nix
+++ b/pkgs/development/libraries/gnome/gnome-mime-data/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, pkgconfig, perl}:
 
-assert !isNull pkgconfig && !isNull perl;
+assert pkgconfig != null && perl != null;
 
 derivation {
   name = "gnome-mime-data-2.4.0";
diff --git a/pkgs/development/libraries/gnome/gnome-vfs/default.nix b/pkgs/development/libraries/gnome/gnome-vfs/default.nix
index a67c2f20deaf..b2cd632f6ce7 100644
--- a/pkgs/development/libraries/gnome/gnome-vfs/default.nix
+++ b/pkgs/development/libraries/gnome/gnome-vfs/default.nix
@@ -1,9 +1,9 @@
 { stdenv, fetchurl, pkgconfig, perl, glib, libxml2, GConf
 , libbonobo, gnomemimedata, popt, bzip2 }:
 
-assert !isNull pkgconfig && !isNull perl && !isNull glib
-  && !isNull libxml2 && !isNull GConf && !isNull libbonobo
-  && !isNull gnomemimedata && !isNull bzip2;
+assert pkgconfig != null && perl != null && glib != null
+  && libxml2 != null && GConf != null && libbonobo != null
+  && gnomemimedata != null && bzip2 != null;
 
 derivation {
   name = "gnome-vfs-2.4.1";
diff --git a/pkgs/development/libraries/gnome/libIDL/default.nix b/pkgs/development/libraries/gnome/libIDL/default.nix
index a7df8988350a..e6ab1cb019b4 100644
--- a/pkgs/development/libraries/gnome/libIDL/default.nix
+++ b/pkgs/development/libraries/gnome/libIDL/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, pkgconfig, glib, lex, yacc}:
 
-assert !isNull pkgconfig && !isNull glib && !isNull lex && !isNull yacc;
+assert pkgconfig != null && glib != null && lex != null && yacc != null;
 
 derivation {
   name = "libIDL-0.8.2";
diff --git a/pkgs/development/libraries/gnome/libbonobo/default.nix b/pkgs/development/libraries/gnome/libbonobo/default.nix
index 9e50e61ac848..c2a6adb9ecef 100644
--- a/pkgs/development/libraries/gnome/libbonobo/default.nix
+++ b/pkgs/development/libraries/gnome/libbonobo/default.nix
@@ -1,7 +1,7 @@
 {stdenv, fetchurl, pkgconfig, perl, ORBit2, libxml2, popt, yacc, flex}:
 
-assert !isNull pkgconfig && !isNull perl && !isNull ORBit2
-  && !isNull libxml2 && !isNull popt && !isNull yacc && !isNull flex;
+assert pkgconfig != null && perl != null && ORBit2 != null
+  && libxml2 != null && popt != null && yacc != null && flex != null;
 
 derivation {
   name = "libbonobo-2.4.2";
diff --git a/pkgs/development/libraries/gnome/libbonoboui/default.nix b/pkgs/development/libraries/gnome/libbonoboui/default.nix
index 8abe0bee2a1f..3efa13fe151d 100644
--- a/pkgs/development/libraries/gnome/libbonoboui/default.nix
+++ b/pkgs/development/libraries/gnome/libbonoboui/default.nix
@@ -1,8 +1,8 @@
 {stdenv, fetchurl, pkgconfig, perl, libxml2, libglade, libgnome
 , libgnomecanvas}:
 
-assert !isNull pkgconfig && !isNull perl && !isNull libxml2
-  && !isNull libglade && !isNull libgnome && !isNull libgnomecanvas;
+assert pkgconfig != null && perl != null && libxml2 != null
+  && libglade != null && libgnome != null && libgnomecanvas != null;
 
 derivation {
   name = "libbonoboui-2.4.1";
diff --git a/pkgs/development/libraries/gnome/libglade/default.nix b/pkgs/development/libraries/gnome/libglade/default.nix
index a8d1cc658270..543586eb20a5 100644
--- a/pkgs/development/libraries/gnome/libglade/default.nix
+++ b/pkgs/development/libraries/gnome/libglade/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, pkgconfig, gtk, libxml2}:
 
-assert !isNull pkgconfig && !isNull gtk && !isNull libxml2;
+assert pkgconfig != null && gtk != null && libxml2 != null;
 
 derivation {
   name = "libglade-2.0.1";
diff --git a/pkgs/development/libraries/gnome/libgnome/default.nix b/pkgs/development/libraries/gnome/libgnome/default.nix
index 35c43c67a151..d33a54cf7a28 100644
--- a/pkgs/development/libraries/gnome/libgnome/default.nix
+++ b/pkgs/development/libraries/gnome/libgnome/default.nix
@@ -1,9 +1,9 @@
 { stdenv, fetchurl, pkgconfig, perl, glib, gnomevfs, libbonobo
 , GConf, popt, zlib }:
 
-assert !isNull pkgconfig && !isNull perl && !isNull glib
-  && !isNull gnomevfs && !isNull libbonobo && !isNull GConf
-  && !isNull popt && !isNull zlib;
+assert pkgconfig != null && perl != null && glib != null
+  && gnomevfs != null && libbonobo != null && GConf != null
+  && popt != null && zlib != null;
 
 # !!! TO CHECK:
 # libgnome tries to install stuff into GConf (which fails):
diff --git a/pkgs/development/libraries/gnome/libgnomecanvas/default.nix b/pkgs/development/libraries/gnome/libgnomecanvas/default.nix
index 4802da9dab99..fef31114b1b8 100644
--- a/pkgs/development/libraries/gnome/libgnomecanvas/default.nix
+++ b/pkgs/development/libraries/gnome/libgnomecanvas/default.nix
@@ -1,7 +1,7 @@
 {stdenv, fetchurl, pkgconfig, gtk, libart, libglade}:
 
-assert !isNull pkgconfig && !isNull gtk && !isNull libart
-  && !isNull libglade;
+assert pkgconfig != null && gtk != null && libart != null
+  && libglade != null;
 
 derivation {
   name = "libgnomecanvas-2.4.0";
diff --git a/pkgs/development/libraries/gnome/libgnomeui/default.nix b/pkgs/development/libraries/gnome/libgnomeui/default.nix
index 23f6b5e5b2df..9a97d7697a95 100644
--- a/pkgs/development/libraries/gnome/libgnomeui/default.nix
+++ b/pkgs/development/libraries/gnome/libgnomeui/default.nix
@@ -1,7 +1,7 @@
 { stdenv, fetchurl, pkgconfig, libgnome, libgnomecanvas, libbonoboui, libglade }:
 
-assert !isNull pkgconfig && !isNull libgnome && !isNull libgnomecanvas
-  && !isNull libbonoboui && !isNull libglade;
+assert pkgconfig != null && libgnome != null && libgnomecanvas != null
+  && libbonoboui != null && libglade != null;
 
 derivation {
   name = "libgnomeui-2.4.0.1";
diff --git a/pkgs/development/libraries/gtk+-1/gdk-pixbuf/default.nix b/pkgs/development/libraries/gtk+-1/gdk-pixbuf/default.nix
index 1b05fdb0ea43..dbf194171c93 100644
--- a/pkgs/development/libraries/gtk+-1/gdk-pixbuf/default.nix
+++ b/pkgs/development/libraries/gtk+-1/gdk-pixbuf/default.nix
@@ -1,7 +1,7 @@
 {stdenv, fetchurl, gtk, libtiff, libjpeg, libpng}:
 
-assert !isNull gtk && !isNull libtiff
-  && !isNull libjpeg && !isNull libpng;
+assert gtk != null && libtiff != null
+  && libjpeg != null && libpng != null;
 
 derivation {
   name = "gdk-pixbuf-0.22.0";
diff --git a/pkgs/development/libraries/gtk+-1/gtk+/default.nix b/pkgs/development/libraries/gtk+-1/gtk+/default.nix
index fc8f45736d97..7ee815ec5f68 100644
--- a/pkgs/development/libraries/gtk+-1/gtk+/default.nix
+++ b/pkgs/development/libraries/gtk+-1/gtk+/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, x11, glib}:
 
-assert !isNull x11 && !isNull glib;
+assert x11 != null && glib != null;
 assert x11.buildClientLibs;
 
 derivation {
diff --git a/pkgs/development/libraries/gtk+/atk/default.nix b/pkgs/development/libraries/gtk+/atk/default.nix
index 8db047f9c492..7d45fbca050e 100644
--- a/pkgs/development/libraries/gtk+/atk/default.nix
+++ b/pkgs/development/libraries/gtk+/atk/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, pkgconfig, glib, perl}:
 
-assert !isNull pkgconfig && !isNull glib && !isNull perl;
+assert pkgconfig != null && glib != null && perl != null;
 
 derivation {
   name = "atk-1.2.4";
diff --git a/pkgs/development/libraries/gtk+/glib/default.nix b/pkgs/development/libraries/gtk+/glib/default.nix
index 227aa80f17d2..88bb12593735 100644
--- a/pkgs/development/libraries/gtk+/glib/default.nix
+++ b/pkgs/development/libraries/gtk+/glib/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, pkgconfig, gettext, perl}:
 
-assert !isNull pkgconfig && !isNull gettext && !isNull perl;
+assert pkgconfig != null && gettext != null && perl != null;
 
 derivation {
   name = "glib-2.2.3";
diff --git a/pkgs/development/libraries/gtk+/gtk+/default.nix b/pkgs/development/libraries/gtk+/gtk+/default.nix
index f0fe5979d0b7..1437221c813c 100644
--- a/pkgs/development/libraries/gtk+/gtk+/default.nix
+++ b/pkgs/development/libraries/gtk+/gtk+/default.nix
@@ -1,9 +1,9 @@
 { stdenv, fetchurl, pkgconfig, x11, glib, atk
 , pango, perl, libtiff, libjpeg, libpng}:
 
-assert !isNull pkgconfig && !isNull x11 && !isNull glib && !isNull atk
-  && !isNull pango && !isNull perl && !isNull perl && !isNull libtiff
-  && !isNull libjpeg && !isNull libpng;
+assert pkgconfig != null && x11 != null && glib != null && atk != null
+  && pango != null && perl != null && perl != null && libtiff != null
+  && libjpeg != null && libpng != null;
 assert x11.buildClientLibs;
 assert glib == atk.glib;
 assert glib == pango.glib;
diff --git a/pkgs/development/libraries/gtk+/pango/default.nix b/pkgs/development/libraries/gtk+/pango/default.nix
index d598d97f9c37..36731123e56f 100644
--- a/pkgs/development/libraries/gtk+/pango/default.nix
+++ b/pkgs/development/libraries/gtk+/pango/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, pkgconfig, x11, glib, xft}:
 
-assert !isNull pkgconfig && !isNull x11 && !isNull glib && !isNull xft;
+assert pkgconfig != null && x11 != null && glib != null && xft != null;
 assert x11.buildClientLibs;
 assert xft.x11 == x11;
 
diff --git a/pkgs/development/libraries/libdvdplay/default.nix b/pkgs/development/libraries/libdvdplay/default.nix
index b038d0e77dbb..7c4d67dbb021 100644
--- a/pkgs/development/libraries/libdvdplay/default.nix
+++ b/pkgs/development/libraries/libdvdplay/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, libdvdread}:
 
-assert !isNull libdvdread;
+assert libdvdread != null;
 
 derivation {
   name = "libdvdplay-1.0.1";
diff --git a/pkgs/development/libraries/libdvdread/default.nix b/pkgs/development/libraries/libdvdread/default.nix
index 6c4f782d237b..11da28b6f854 100644
--- a/pkgs/development/libraries/libdvdread/default.nix
+++ b/pkgs/development/libraries/libdvdread/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, libdvdcss}:
 
-assert !isNull libdvdcss;
+assert libdvdcss != null;
 
 derivation {
   name = "libdvdread-20030812";
diff --git a/pkgs/development/libraries/libpng/default.nix b/pkgs/development/libraries/libpng/default.nix
index 47322de7d175..5e0d65dc02ea 100644
--- a/pkgs/development/libraries/libpng/default.nix
+++ b/pkgs/development/libraries/libpng/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, zlib}:
 
-assert !isNull zlib;
+assert zlib != null;
 
 derivation {
   name = "libpng-1.2.5";
diff --git a/pkgs/development/libraries/libtiff/default.nix b/pkgs/development/libraries/libtiff/default.nix
index 7a14a63ce337..7b16f5f067ce 100644
--- a/pkgs/development/libraries/libtiff/default.nix
+++ b/pkgs/development/libraries/libtiff/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, zlib, libjpeg}:
 
-assert !isNull zlib && !isNull libjpeg;
+assert zlib != null && libjpeg != null;
 
 derivation {
   name = "libtiff-3.5.7";
diff --git a/pkgs/development/libraries/libxml2/default.nix b/pkgs/development/libraries/libxml2/default.nix
index 4eb33f53d012..7533451029e3 100644
--- a/pkgs/development/libraries/libxml2/default.nix
+++ b/pkgs/development/libraries/libxml2/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, zlib}:
 
-assert !isNull zlib;
+assert zlib != null;
 
 derivation {
   name = "libxml2-2.6.7";
diff --git a/pkgs/development/libraries/libxslt/default.nix b/pkgs/development/libraries/libxslt/default.nix
index 0d9b29fb309b..b005aca4aaf9 100644
--- a/pkgs/development/libraries/libxslt/default.nix
+++ b/pkgs/development/libraries/libxslt/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, libxml2}:
 
-assert !isNull libxml2;
+assert libxml2 != null;
 
 derivation {
   name = "libxslt-1.1.0";
diff --git a/pkgs/development/libraries/popt/default.nix b/pkgs/development/libraries/popt/default.nix
index 11cc43d48f8b..7ad1cb807b7c 100644
--- a/pkgs/development/libraries/popt/default.nix
+++ b/pkgs/development/libraries/popt/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, gettext}:
 
-assert !isNull gettext;
+assert gettext != null;
 
 derivation {
   name = "popt-1.7";
diff --git a/pkgs/development/libraries/scrollkeeper/default.nix b/pkgs/development/libraries/scrollkeeper/default.nix
index 33cd0489af2e..5d86dff1e0e1 100644
--- a/pkgs/development/libraries/scrollkeeper/default.nix
+++ b/pkgs/development/libraries/scrollkeeper/default.nix
@@ -1,8 +1,8 @@
 { stdenv, fetchurl, perl, libxml2, libxslt, docbook_xml_dtd
 , perlXMLParser}:
 
-assert !isNull perl && !isNull libxml2 && !isNull libxslt
-  && !isNull docbook_xml_dtd && !isNull perlXMLParser;
+assert perl != null && libxml2 != null && libxslt != null
+  && docbook != null_xml_dtd && perlXMLParser != null;
 
 # !!! seems to need iconv, but cannot find it since $glibc/bin is not in PATH
 
diff --git a/pkgs/development/libraries/wxGTK/default.nix b/pkgs/development/libraries/wxGTK/default.nix
index 0645de6495d7..039579c2d543 100644
--- a/pkgs/development/libraries/wxGTK/default.nix
+++ b/pkgs/development/libraries/wxGTK/default.nix
@@ -1,10 +1,10 @@
 {stdenv, fetchurl, pkgconfig, gtk, compat22 ? true}:
 
-assert !isNull pkgconfig && !isNull gtk;
-assert !isNull gtk.libtiff;
-assert !isNull gtk.libjpeg;
-assert !isNull gtk.libpng;
-assert !isNull gtk.libpng.zlib;
+assert pkgconfig != null && gtk != null;
+assert gtk.libtiff != null;
+assert gtk.libjpeg != null;
+assert gtk.libpng != null;
+assert gtk.libpng.zlib != null;
 
 derivation {
   name = "wxGTK-2.4.2";
diff --git a/pkgs/development/libraries/xft/default.nix b/pkgs/development/libraries/xft/default.nix
index 0764a1dd80ad..ea1cef2cfe6d 100644
--- a/pkgs/development/libraries/xft/default.nix
+++ b/pkgs/development/libraries/xft/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, pkgconfig, x11, fontconfig}:
 
-assert !isNull pkgconfig && !isNull x11 && !isNull fontconfig;
+assert pkgconfig != null && x11 != null && fontconfig != null;
 assert fontconfig.x11 == x11;
 
 derivation {
diff --git a/pkgs/development/libraries/zvbi/default.nix b/pkgs/development/libraries/zvbi/default.nix
index 55a106b349e3..54de0c92816a 100644
--- a/pkgs/development/libraries/zvbi/default.nix
+++ b/pkgs/development/libraries/zvbi/default.nix
@@ -1,8 +1,8 @@
 { pngSupport ? true
 , stdenv, fetchurl, x11, libpng ? null}:
 
-assert !isNull x11;
-assert pngSupport -> !isNull libpng;
+assert x11 != null;
+assert pngSupport -> libpng != null;
 
 derivation {
   name = "zvbi-0.2.5";
diff --git a/pkgs/development/perl-modules/BerkeleyDB/default.nix b/pkgs/development/perl-modules/BerkeleyDB/default.nix
index 1e94e5da8fed..8dd44e1e201c 100644
--- a/pkgs/development/perl-modules/BerkeleyDB/default.nix
+++ b/pkgs/development/perl-modules/BerkeleyDB/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, perl, db4}:
 
-assert !isNull perl && !isNull db4;
+assert perl != null && db4 != null;
 
 derivation {
   name = "perl-BerkeleyDB-0.25";
diff --git a/pkgs/development/perl-modules/XML-Parser/default.nix b/pkgs/development/perl-modules/XML-Parser/default.nix
index 0c0311962ba1..79bad03171ec 100644
--- a/pkgs/development/perl-modules/XML-Parser/default.nix
+++ b/pkgs/development/perl-modules/XML-Parser/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, perl, expat}:
 
-assert !isNull perl && !isNull expat;
+assert perl != null && expat != null;
 
 derivation {
   name = "perl-XML-Parser-2.34";
diff --git a/pkgs/development/tools/misc/swig/default.nix b/pkgs/development/tools/misc/swig/default.nix
index de5048afba15..a84ad4fc1f35 100644
--- a/pkgs/development/tools/misc/swig/default.nix
+++ b/pkgs/development/tools/misc/swig/default.nix
@@ -1,8 +1,8 @@
 { perlSupport, pythonSupport
 , stdenv, fetchurl, perl ? null, python ? null}:
 
-assert perlSupport -> !isNull perl;
-assert pythonSupport -> !isNull python;
+assert perlSupport -> perl != null;
+assert pythonSupport -> python != null;
 
 derivation {
   name = "swig-1.3.19";
diff --git a/pkgs/development/tools/parsing/bison/bison-new.nix b/pkgs/development/tools/parsing/bison/bison-new.nix
index b8e3596e7943..43f66ce06a9c 100644
--- a/pkgs/development/tools/parsing/bison/bison-new.nix
+++ b/pkgs/development/tools/parsing/bison/bison-new.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, m4}:
 
-assert !isNull m4;
+assert m4 != null;
 
 derivation {
   name = "bison-1.875c";
diff --git a/pkgs/development/tools/parsing/bison/default.nix b/pkgs/development/tools/parsing/bison/default.nix
index fc8941b76f34..085b1e0f6364 100644
--- a/pkgs/development/tools/parsing/bison/default.nix
+++ b/pkgs/development/tools/parsing/bison/default.nix
@@ -1,5 +1,5 @@
 {stdenv, fetchurl, m4}:
-assert !isNull m4;
+assert m4 != null;
 derivation {
   name = "bison-1.875";
   system = stdenv.system;
diff --git a/pkgs/development/tools/parsing/flex/default.nix b/pkgs/development/tools/parsing/flex/default.nix
index 605c29db2d22..3a4e3649e002 100644
--- a/pkgs/development/tools/parsing/flex/default.nix
+++ b/pkgs/development/tools/parsing/flex/default.nix
@@ -1,5 +1,5 @@
 {stdenv, fetchurl, yacc}:
-assert !isNull yacc;
+assert yacc != null;
 derivation {
   name = "flex-2.5.4a";
   system = stdenv.system;
diff --git a/pkgs/development/tools/parsing/flex/flex-new.nix b/pkgs/development/tools/parsing/flex/flex-new.nix
index cc769faaac44..6da54271823b 100644
--- a/pkgs/development/tools/parsing/flex/flex-new.nix
+++ b/pkgs/development/tools/parsing/flex/flex-new.nix
@@ -3,7 +3,7 @@
 
 {stdenv, fetchurl, yacc, m4}:
 
-assert !isNull yacc;
+assert yacc != null;
 
 derivation {
   name = "flex-2.5.31";
diff --git a/pkgs/servers/x11/xfree86/default.nix b/pkgs/servers/x11/xfree86/default.nix
index 17971c2081fd..1de8e2b9a117 100644
--- a/pkgs/servers/x11/xfree86/default.nix
+++ b/pkgs/servers/x11/xfree86/default.nix
@@ -4,7 +4,7 @@
 
 assert !buildServer; # we don't support this currently
 assert buildClientLibs; # we don't support *not* doing this currently
-assert !isNull bison && !isNull flex;
+assert bison != null && flex != null;
 
 derivation {
   name = "xfree86-4.3";
diff --git a/pkgs/tools/graphics/graphviz/default.nix b/pkgs/tools/graphics/graphviz/default.nix
index b1689ec234ed..9bc51be695a9 100644
--- a/pkgs/tools/graphics/graphviz/default.nix
+++ b/pkgs/tools/graphics/graphviz/default.nix
@@ -1,7 +1,7 @@
 {stdenv, fetchurl, x11, libpng, libjpeg, expat}:
 
-assert !isNull x11 && !isNull libpng && !isNull libjpeg
-  && !isNull expat;
+assert x11 != null && libpng != null && libjpeg != null
+  && expat != null;
 
 derivation {
   name = "graphviz-1.10";