From d10e69c86bcd415f5c4347d3c6b981241e913465 Mon Sep 17 00:00:00 2001
From: Felix Buehler <account@buehler.rocks>
Date: Sun, 5 Mar 2023 22:08:45 +0100
Subject: [PATCH] treewide: deprecate isNull

https://nixos.org/manual/nix/stable/language/builtins.html#builtins-isNull
---
 lib/generators.nix                                 |  2 +-
 maintainers/scripts/haskell/dependencies.nix       |  2 +-
 nixos/modules/hardware/device-tree.nix             |  8 ++++----
 nixos/modules/security/doas.nix                    |  6 +++---
 nixos/modules/security/pam.nix                     |  4 ++--
 nixos/modules/services/cluster/kubernetes/pki.nix  |  2 +-
 nixos/modules/services/hardware/undervolt.nix      |  4 ++--
 .../services/home-automation/home-assistant.nix    |  2 +-
 nixos/modules/services/networking/multipath.nix    |  8 ++++----
 nixos/modules/services/networking/radicale.nix     |  6 +++---
 nixos/modules/services/system/self-deploy.nix      |  2 +-
 nixos/modules/services/web-apps/dolibarr.nix       |  2 +-
 nixos/modules/services/web-apps/writefreely.nix    | 11 +++++------
 .../editors/emacs/elisp-packages/libgenerated.nix  | 14 +++++++-------
 pkgs/applications/science/logic/coq/default.nix    |  2 +-
 .../virtualization/singularity/generic.nix         |  6 +++---
 pkgs/build-support/coq/default.nix                 |  2 +-
 pkgs/build-support/coq/meta-fetch/default.nix      |  8 ++++----
 pkgs/build-support/make-desktopitem/default.nix    |  2 +-
 pkgs/data/themes/orchis-theme/default.nix          |  2 +-
 .../nim-packages/build-nim-package/default.nix     |  8 ++++----
 pkgs/development/python-modules/mip/default.nix    |  4 ++--
 .../tools/build-managers/waf/default.nix           |  2 +-
 .../poetry2nix/poetry2nix/overrides/default.nix    |  2 +-
 pkgs/games/cataclysm-dda/pkgs/default.nix          |  2 +-
 pkgs/games/curseofwar/default.nix                  |  2 +-
 pkgs/servers/nosql/arangodb/default.nix            |  2 +-
 pkgs/stdenv/generic/make-derivation.nix            |  2 +-
 pkgs/tools/misc/plfit/default.nix                  |  4 ++--
 pkgs/tools/text/gawk/gawkextlib.nix                |  2 +-
 30 files changed, 62 insertions(+), 63 deletions(-)

diff --git a/lib/generators.nix b/lib/generators.nix
index 968331a0ebde..4357a0353398 100644
--- a/lib/generators.nix
+++ b/lib/generators.nix
@@ -422,7 +422,7 @@ ${expr "" v}
       (if v then "True" else "False")
     else if isFunction v then
       abort "generators.toDhall: cannot convert a function to Dhall"
-    else if isNull v then
+    else if v == null then
       abort "generators.toDhall: cannot convert a null to Dhall"
     else
       builtins.toJSON v;
diff --git a/maintainers/scripts/haskell/dependencies.nix b/maintainers/scripts/haskell/dependencies.nix
index f0620902c0ee..fd8338c0029a 100644
--- a/maintainers/scripts/haskell/dependencies.nix
+++ b/maintainers/scripts/haskell/dependencies.nix
@@ -3,7 +3,7 @@ let
   pkgs = import ../../.. {};
   inherit (pkgs) lib;
   getDeps = _: pkg: {
-    deps = builtins.filter (x: !isNull x) (map (x: x.pname or null) (pkg.propagatedBuildInputs or []));
+    deps = builtins.filter (x: x != null) (map (x: x.pname or null) (pkg.propagatedBuildInputs or []));
     broken = (pkg.meta.hydraPlatforms or [null]) == [];
   };
 in
diff --git a/nixos/modules/hardware/device-tree.nix b/nixos/modules/hardware/device-tree.nix
index 2807313a5a9c..c568f52ab677 100644
--- a/nixos/modules/hardware/device-tree.nix
+++ b/nixos/modules/hardware/device-tree.nix
@@ -65,7 +65,7 @@ let
     };
   };
 
-  filterDTBs = src: if isNull cfg.filter
+  filterDTBs = src: if cfg.filter == null
     then "${src}/dtbs"
     else
       pkgs.runCommand "dtbs-filtered" {} ''
@@ -93,8 +93,8 @@ let
   # Fill in `dtboFile` for each overlay if not set already.
   # Existence of one of these is guarded by assertion below
   withDTBOs = xs: flip map xs (o: o // { dtboFile =
-    if isNull o.dtboFile then
-      if !isNull o.dtsFile then compileDTS o.name o.dtsFile
+    if o.dtboFile == null then
+      if o.dtsFile != null then compileDTS o.name o.dtsFile
       else compileDTS o.name (pkgs.writeText "dts" o.dtsText)
     else o.dtboFile; } );
 
@@ -181,7 +181,7 @@ in
   config = mkIf (cfg.enable) {
 
     assertions = let
-      invalidOverlay = o: isNull o.dtsFile && isNull o.dtsText && isNull o.dtboFile;
+      invalidOverlay = o: (o.dtsFile == null) && (o.dtsText == null) && (o.dtboFile == null);
     in lib.singleton {
       assertion = lib.all (o: !invalidOverlay o) cfg.overlays;
       message = ''
diff --git a/nixos/modules/security/doas.nix b/nixos/modules/security/doas.nix
index 4d15ed9a8025..be30a6b92e26 100644
--- a/nixos/modules/security/doas.nix
+++ b/nixos/modules/security/doas.nix
@@ -19,7 +19,7 @@ let
   ];
 
   mkArgs = rule:
-    if (isNull rule.args) then ""
+    if (rule.args == null) then ""
     else if (length rule.args == 0) then "args"
     else "args ${concatStringsSep " " rule.args}";
 
@@ -27,9 +27,9 @@ let
     let
       opts = mkOpts rule;
 
-      as = optionalString (!isNull rule.runAs) "as ${rule.runAs}";
+      as = optionalString (rule.runAs != null) "as ${rule.runAs}";
 
-      cmd = optionalString (!isNull rule.cmd) "cmd ${rule.cmd}";
+      cmd = optionalString (rule.cmd != null) "cmd ${rule.cmd}";
 
       args = mkArgs rule;
     in
diff --git a/nixos/modules/security/pam.nix b/nixos/modules/security/pam.nix
index 4224722f8792..9b00b91e1281 100644
--- a/nixos/modules/security/pam.nix
+++ b/nixos/modules/security/pam.nix
@@ -793,7 +793,7 @@ let
     };
   }));
 
-  motd = if isNull config.users.motdFile
+  motd = if config.users.motdFile == null
          then pkgs.writeText "motd" config.users.motd
          else config.users.motdFile;
 
@@ -1233,7 +1233,7 @@ in
   config = {
     assertions = [
       {
-        assertion = isNull config.users.motd || isNull config.users.motdFile;
+        assertion = config.users.motd == null || config.users.motdFile == null;
         message = ''
           Only one of users.motd and users.motdFile can be set.
         '';
diff --git a/nixos/modules/services/cluster/kubernetes/pki.nix b/nixos/modules/services/cluster/kubernetes/pki.nix
index 26fe0f5e9e09..38682701ea15 100644
--- a/nixos/modules/services/cluster/kubernetes/pki.nix
+++ b/nixos/modules/services/cluster/kubernetes/pki.nix
@@ -270,7 +270,7 @@ in
           '';
         })]);
 
-      environment.etc.${cfg.etcClusterAdminKubeconfig}.source = mkIf (!isNull cfg.etcClusterAdminKubeconfig)
+      environment.etc.${cfg.etcClusterAdminKubeconfig}.source = mkIf (cfg.etcClusterAdminKubeconfig != null)
         clusterAdminKubeconfig;
 
       environment.systemPackages = mkIf (top.kubelet.enable || top.proxy.enable) [
diff --git a/nixos/modules/services/hardware/undervolt.nix b/nixos/modules/services/hardware/undervolt.nix
index c49d944cdc18..944777475401 100644
--- a/nixos/modules/services/hardware/undervolt.nix
+++ b/nixos/modules/services/hardware/undervolt.nix
@@ -5,8 +5,8 @@ let
   cfg = config.services.undervolt;
 
   mkPLimit = limit: window:
-    if (isNull limit && isNull window) then null
-    else assert asserts.assertMsg (!isNull limit && !isNull window) "Both power limit and window must be set";
+    if (limit == null && window == null) then null
+    else assert asserts.assertMsg (limit != null && window != null) "Both power limit and window must be set";
       "${toString limit} ${toString window}";
   cliArgs = lib.cli.toGNUCommandLine {} {
     inherit (cfg)
diff --git a/nixos/modules/services/home-automation/home-assistant.nix b/nixos/modules/services/home-automation/home-assistant.nix
index 6adc58ec58ec..cea8a2b14cc2 100644
--- a/nixos/modules/services/home-automation/home-assistant.nix
+++ b/nixos/modules/services/home-automation/home-assistant.nix
@@ -362,7 +362,7 @@ in {
   config = mkIf cfg.enable {
     assertions = [
       {
-        assertion = cfg.openFirewall -> !isNull cfg.config;
+        assertion = cfg.openFirewall -> cfg.config != null;
         message = "openFirewall can only be used with a declarative config";
       }
     ];
diff --git a/nixos/modules/services/networking/multipath.nix b/nixos/modules/services/networking/multipath.nix
index b20ec76ddf59..bd403e109c2a 100644
--- a/nixos/modules/services/networking/multipath.nix
+++ b/nixos/modules/services/networking/multipath.nix
@@ -513,22 +513,22 @@ in {
         ${indentLines 2 devices}
         }
 
-        ${optionalString (!isNull defaults) ''
+        ${optionalString (defaults != null) ''
           defaults {
           ${indentLines 2 defaults}
           }
         ''}
-        ${optionalString (!isNull blacklist) ''
+        ${optionalString (blacklist != null) ''
           blacklist {
           ${indentLines 2 blacklist}
           }
         ''}
-        ${optionalString (!isNull blacklist_exceptions) ''
+        ${optionalString (blacklist_exceptions != null) ''
           blacklist_exceptions {
           ${indentLines 2 blacklist_exceptions}
           }
         ''}
-        ${optionalString (!isNull overrides) ''
+        ${optionalString (overrides != null) ''
           overrides {
           ${indentLines 2 overrides}
           }
diff --git a/nixos/modules/services/networking/radicale.nix b/nixos/modules/services/networking/radicale.nix
index 8e4789c7ca59..00dbd6bbe386 100644
--- a/nixos/modules/services/networking/radicale.nix
+++ b/nixos/modules/services/networking/radicale.nix
@@ -9,7 +9,7 @@ let
     listToValue = concatMapStringsSep ", " (generators.mkValueStringDefault { });
   };
 
-  pkg = if isNull cfg.package then
+  pkg = if cfg.package == null then
     pkgs.radicale
   else
     cfg.package;
@@ -117,13 +117,13 @@ in {
       }
     ];
 
-    warnings = optional (isNull cfg.package && versionOlder config.system.stateVersion "17.09") ''
+    warnings = optional (cfg.package == null && versionOlder config.system.stateVersion "17.09") ''
       The configuration and storage formats of your existing Radicale
       installation might be incompatible with the newest version.
       For upgrade instructions see
       https://radicale.org/2.1.html#documentation/migration-from-1xx-to-2xx.
       Set services.radicale.package to suppress this warning.
-    '' ++ optional (isNull cfg.package && versionOlder config.system.stateVersion "20.09") ''
+    '' ++ optional (cfg.package == null && versionOlder config.system.stateVersion "20.09") ''
       The configuration format of your existing Radicale installation might be
       incompatible with the newest version.  For upgrade instructions see
       https://github.com/Kozea/Radicale/blob/3.0.6/NEWS.md#upgrade-checklist.
diff --git a/nixos/modules/services/system/self-deploy.nix b/nixos/modules/services/system/self-deploy.nix
index 16a793a42253..5f9ee06124cb 100644
--- a/nixos/modules/services/system/self-deploy.nix
+++ b/nixos/modules/services/system/self-deploy.nix
@@ -132,7 +132,7 @@ in
 
       requires = lib.mkIf (!(isPathType cfg.repository)) [ "network-online.target" ];
 
-      environment.GIT_SSH_COMMAND = lib.mkIf (!(isNull cfg.sshKeyFile))
+      environment.GIT_SSH_COMMAND = lib.mkIf (cfg.sshKeyFile != null)
         "${pkgs.openssh}/bin/ssh -i ${lib.escapeShellArg cfg.sshKeyFile}";
 
       restartIfChanged = false;
diff --git a/nixos/modules/services/web-apps/dolibarr.nix b/nixos/modules/services/web-apps/dolibarr.nix
index f262099354d2..473ec7b1d4b0 100644
--- a/nixos/modules/services/web-apps/dolibarr.nix
+++ b/nixos/modules/services/web-apps/dolibarr.nix
@@ -16,7 +16,7 @@ let
         if (any (str: k == str) secretKeys) then v
         else if isString v then "'${v}'"
         else if isBool v then boolToString v
-        else if isNull v then "null"
+        else if v == null then "null"
         else toString v
       ;
     in
diff --git a/nixos/modules/services/web-apps/writefreely.nix b/nixos/modules/services/web-apps/writefreely.nix
index dec00b46f335..a7671aa717f4 100644
--- a/nixos/modules/services/web-apps/writefreely.nix
+++ b/nixos/modules/services/web-apps/writefreely.nix
@@ -10,12 +10,11 @@ let
   format = pkgs.formats.ini {
     mkKeyValue = key: value:
       let
-        value' = if builtins.isNull value then
-          ""
-        else if builtins.isBool value then
-          if value == true then "true" else "false"
-        else
-          toString value;
+        value' = lib.optionalString (value != null)
+          (if builtins.isBool value then
+            if value == true then "true" else "false"
+          else
+            toString value);
       in "${key} = ${value'}";
   };
 
diff --git a/pkgs/applications/editors/emacs/elisp-packages/libgenerated.nix b/pkgs/applications/editors/emacs/elisp-packages/libgenerated.nix
index f45aadfa67b4..36576f7c1239 100644
--- a/pkgs/applications/editors/emacs/elisp-packages/libgenerated.nix
+++ b/pkgs/applications/editors/emacs/elisp-packages/libgenerated.nix
@@ -73,28 +73,28 @@ in {
         error = sourceArgs.error or args.error or null;
         hasSource = lib.hasAttr variant args;
         pname = builtins.replaceStrings [ "@" ] [ "at" ] ename;
-        broken = ! isNull error;
+        broken = error != null;
       in
       if hasSource then
         lib.nameValuePair ename (
           self.callPackage ({ melpaBuild, fetchurl, ... }@pkgargs:
           melpaBuild {
             inherit pname ename commit;
-            version = if isNull version then "" else
-              lib.concatStringsSep "." (map toString
+            version = lib.optionalString (version != null)
+              (lib.concatStringsSep "." (map toString
                 # Hack: Melpa archives contains versions with parse errors such as [ 4 4 -4 413 ] which should be 4.4-413
                 # This filter method is still technically wrong, but it's computationally cheap enough and tapers over the issue
-                (builtins.filter (n: n >= 0) version));
+                (builtins.filter (n: n >= 0) version)));
             # TODO: Broken should not result in src being null (hack to avoid eval errors)
-            src = if (isNull sha256 || broken) then null else
+            src = if (sha256 == null || broken) then null else
               lib.getAttr fetcher (fetcherGenerators args sourceArgs);
-            recipe = if isNull commit then null else
+            recipe = if commit == null then null else
               fetchurl {
                 name = pname + "-recipe";
                 url = "https://raw.githubusercontent.com/melpa/melpa/${commit}/recipes/${ename}";
                 inherit sha256;
               };
-            packageRequires = lib.optionals (! isNull deps)
+            packageRequires = lib.optionals (deps != null)
               (map (dep: pkgargs.${dep} or self.${dep} or null)
                    deps);
             meta = (sourceArgs.meta or {}) // {
diff --git a/pkgs/applications/science/logic/coq/default.nix b/pkgs/applications/science/logic/coq/default.nix
index 49c9fc47fef2..3740d4e39268 100644
--- a/pkgs/applications/science/logic/coq/default.nix
+++ b/pkgs/applications/science/logic/coq/default.nix
@@ -70,7 +70,7 @@ let
     substituteInPlace plugins/micromega/sos.ml --replace "; csdp" "; ${csdp}/bin/csdp"
     substituteInPlace plugins/micromega/coq_micromega.ml --replace "System.is_in_system_path \"csdp\"" "true"
   '';
-  ocamlPackages = if !isNull customOCamlPackages then customOCamlPackages
+  ocamlPackages = if customOCamlPackages != null then customOCamlPackages
     else with versions; switch coq-version [
       { case = range "8.16" "8.17"; out = ocamlPackages_4_14; }
       { case = range "8.14" "8.15"; out = ocamlPackages_4_12; }
diff --git a/pkgs/applications/virtualization/singularity/generic.nix b/pkgs/applications/virtualization/singularity/generic.nix
index f20735e45e3d..5312dbdda0ff 100644
--- a/pkgs/applications/virtualization/singularity/generic.nix
+++ b/pkgs/applications/virtualization/singularity/generic.nix
@@ -76,7 +76,7 @@ in
 
 let
   defaultPathOriginal = "/bin:/usr/bin:/sbin:/usr/sbin:/usr/local/bin:/usr/local/sbin";
-  privileged-un-utils = if ((isNull newuidmapPath) && (isNull newgidmapPath)) then null else
+  privileged-un-utils = if ((newuidmapPath == null) && (newgidmapPath == null)) then null else
   (runCommandLocal "privileged-un-utils" { } ''
     mkdir -p "$out/bin"
     ln -s ${lib.escapeShellArg newuidmapPath} "$out/bin/newuidmap"
@@ -212,10 +212,10 @@ buildGoModule {
         rm "$file"
       done
     ''}
-    ${lib.optionalString enableSuid (lib.warnIf (isNull starterSuidPath) "${projectName}: Null starterSuidPath when enableSuid produces non-SUID-ed starter-suid and run-time permission denial." ''
+    ${lib.optionalString enableSuid (lib.warnIf (starterSuidPath == null) "${projectName}: Null starterSuidPath when enableSuid produces non-SUID-ed starter-suid and run-time permission denial." ''
       chmod +x $out/libexec/${projectName}/bin/starter-suid
     '')}
-    ${lib.optionalString (enableSuid && !isNull starterSuidPath) ''
+    ${lib.optionalString (enableSuid && (starterSuidPath != null)) ''
       mv "$out"/libexec/${projectName}/bin/starter-suid{,.orig}
       ln -s ${lib.escapeShellArg starterSuidPath} "$out/libexec/${projectName}/bin/starter-suid"
     ''}
diff --git a/pkgs/build-support/coq/default.nix b/pkgs/build-support/coq/default.nix
index e26504a66f10..eb045ddf6865 100644
--- a/pkgs/build-support/coq/default.nix
+++ b/pkgs/build-support/coq/default.nix
@@ -52,7 +52,7 @@ let
       inherit release releaseRev;
       location = { inherit domain owner repo; };
     } // optionalAttrs (args?fetcher) {inherit fetcher;});
-  fetched = fetch (if !isNull version then version else defaultVersion);
+  fetched = fetch (if version != null then version else defaultVersion);
   display-pkg = n: sep: v:
     let d = displayVersion.${n} or (if sep == "" then ".." else true); in
     n + optionalString (v != "" && v != null) (switch d [
diff --git a/pkgs/build-support/coq/meta-fetch/default.nix b/pkgs/build-support/coq/meta-fetch/default.nix
index d5fe31c6ccf7..82c29fb760b7 100644
--- a/pkgs/build-support/coq/meta-fetch/default.nix
+++ b/pkgs/build-support/coq/meta-fetch/default.nix
@@ -8,13 +8,13 @@ let
         fmt = if args?sha256 then "zip" else "tarball";
         pr  = match "^#(.*)$" rev;
         url = switch-if [
-          { cond = isNull pr && !isNull (match "^github.*" domain);
+          { cond = pr == null && (match "^github.*" domain) != null;
             out = "https://${domain}/${owner}/${repo}/archive/${rev}.${ext}"; }
-          { cond = !isNull pr && !isNull (match "^github.*" domain);
+          { cond = pr != null && (match "^github.*" domain) != null;
             out = "https://api.${domain}/repos/${owner}/${repo}/${fmt}/pull/${head pr}/head"; }
-          { cond = isNull pr && !isNull (match "^gitlab.*" domain);
+          { cond = pr == null && (match "^gitlab.*" domain) != null;
             out = "https://${domain}/${owner}/${repo}/-/archive/${rev}/${repo}-${rev}.${ext}"; }
-          { cond = !isNull (match "(www.)?mpi-sws.org" domain);
+          { cond = (match "(www.)?mpi-sws.org" domain) != null;
             out = "https://www.mpi-sws.org/~${owner}/${repo}/download/${repo}-${rev}.${ext}";}
         ] (throw "meta-fetch: no fetcher found for domain ${domain} on ${rev}");
         fetch = x: if args?sha256 then fetchzip (x // { inherit sha256; }) else fetchTarball x;
diff --git a/pkgs/build-support/make-desktopitem/default.nix b/pkgs/build-support/make-desktopitem/default.nix
index af314aa338c8..ccceb23256b6 100644
--- a/pkgs/build-support/make-desktopitem/default.nix
+++ b/pkgs/build-support/make-desktopitem/default.nix
@@ -89,7 +89,7 @@ let
   renderSection = sectionName: attrs:
     lib.pipe attrs [
       (lib.mapAttrsToList renderLine)
-      (builtins.filter (v: !isNull v))
+      (builtins.filter (v: v != null))
       (builtins.concatStringsSep "\n")
       (section: ''
         [${sectionName}]
diff --git a/pkgs/data/themes/orchis-theme/default.nix b/pkgs/data/themes/orchis-theme/default.nix
index 840072295aa7..c536b7c53624 100644
--- a/pkgs/data/themes/orchis-theme/default.nix
+++ b/pkgs/data/themes/orchis-theme/default.nix
@@ -45,7 +45,7 @@ rec {
     runHook preInstall
     bash install.sh -d $out/share/themes -t all \
       ${lib.optionalString (tweaks != []) "--tweaks " + builtins.toString tweaks} \
-      ${lib.optionalString (!isNull border-radius) ("--round " + builtins.toString border-radius + "px")}
+      ${lib.optionalString (border-radius != null) ("--round " + builtins.toString border-radius + "px")}
     ${lib.optionalString withWallpapers ''
       mkdir -p $out/share/backgrounds
       cp src/wallpaper/{1080p,2k,4k}.jpg $out/share/backgrounds
diff --git a/pkgs/development/nim-packages/build-nim-package/default.nix b/pkgs/development/nim-packages/build-nim-package/default.nix
index 5ad181252df4..5c64b7b745c2 100644
--- a/pkgs/development/nim-packages/build-nim-package/default.nix
+++ b/pkgs/development/nim-packages/build-nim-package/default.nix
@@ -9,7 +9,7 @@ stdenv.mkDerivation (attrs // {
   depsBuildBuild = [ nim_builder ] ++ depsBuildBuild;
   nativeBuildInputs = [ nim ] ++ nativeBuildInputs;
 
-  configurePhase = if isNull configurePhase then ''
+  configurePhase = if (configurePhase == null) then ''
     runHook preConfigure
     export NIX_NIM_BUILD_INPUTS=''${pkgsHostTarget[@]} $NIX_NIM_BUILD_INPUTS
     nim_builder --phase:configure
@@ -17,21 +17,21 @@ stdenv.mkDerivation (attrs // {
   '' else
     configurePhase;
 
-  buildPhase = if isNull buildPhase then ''
+  buildPhase = if (buildPhase == null) then ''
     runHook preBuild
     nim_builder --phase:build
     runHook postBuild
   '' else
     buildPhase;
 
-  checkPhase = if isNull checkPhase then ''
+  checkPhase = if (checkPhase == null) then ''
     runHook preCheck
     nim_builder --phase:check
     runHook postCheck
   '' else
     checkPhase;
 
-  installPhase = if isNull installPhase then ''
+  installPhase = if (installPhase == null) then ''
     runHook preInstall
     nim_builder --phase:install
     runHook postInstall
diff --git a/pkgs/development/python-modules/mip/default.nix b/pkgs/development/python-modules/mip/default.nix
index 1011677338bf..e2896bf374a2 100644
--- a/pkgs/development/python-modules/mip/default.nix
+++ b/pkgs/development/python-modules/mip/default.nix
@@ -35,7 +35,7 @@ buildPythonPackage rec {
     cffi
   ] ++ lib.optionals gurobiSupport ([
     gurobipy
-  ] ++ lib.optional (builtins.isNull gurobiHome) gurobi);
+  ] ++ lib.optional (gurobiHome == null) gurobi);
 
   # Source files have CRLF terminators, which make patch error out when supplied
   # with diffs made on *nix machines
@@ -58,7 +58,7 @@ buildPythonPackage rec {
 
   # Make MIP use the Gurobi solver, if configured to do so
   makeWrapperArgs = lib.optional gurobiSupport
-    "--set GUROBI_HOME ${if builtins.isNull gurobiHome then gurobi.outPath else gurobiHome}";
+    "--set GUROBI_HOME ${if gurobiHome == null then gurobi.outPath else gurobiHome}";
 
   # Tests that rely on Gurobi are activated only when Gurobi support is enabled
   disabledTests = lib.optional (!gurobiSupport) "gurobi";
diff --git a/pkgs/development/tools/build-managers/waf/default.nix b/pkgs/development/tools/build-managers/waf/default.nix
index 4e42927d0293..218783fd4926 100644
--- a/pkgs/development/tools/build-managers/waf/default.nix
+++ b/pkgs/development/tools/build-managers/waf/default.nix
@@ -4,7 +4,7 @@
 }:
 let
   wafToolsArg = with lib.strings;
-    optionalString (!isNull withTools) " --tools=\"${concatStringsSep "," withTools}\"";
+    optionalString (withTools != null) " --tools=\"${concatStringsSep "," withTools}\"";
 in
 stdenv.mkDerivation rec {
   pname = "waf";
diff --git a/pkgs/development/tools/poetry2nix/poetry2nix/overrides/default.nix b/pkgs/development/tools/poetry2nix/poetry2nix/overrides/default.nix
index a5bb46309f4c..cb5bda0bba76 100644
--- a/pkgs/development/tools/poetry2nix/poetry2nix/overrides/default.nix
+++ b/pkgs/development/tools/poetry2nix/poetry2nix/overrides/default.nix
@@ -50,7 +50,7 @@ let
             {
               nativeBuildInputs =
                 (old.nativeBuildInputs or [ ])
-                ++ lib.optionals (!(builtins.isNull buildSystem)) [ buildSystem ]
+                ++ lib.optionals (buildSystem != null) [ buildSystem ]
                 ++ map (a: self.${a}) extraAttrs;
             }
         )
diff --git a/pkgs/games/cataclysm-dda/pkgs/default.nix b/pkgs/games/cataclysm-dda/pkgs/default.nix
index 39abad809c5b..72b2c814389a 100644
--- a/pkgs/games/cataclysm-dda/pkgs/default.nix
+++ b/pkgs/games/cataclysm-dda/pkgs/default.nix
@@ -16,7 +16,7 @@ let
   pkgs' = lib.mapAttrs (_: mods: lib.filterAttrs isAvailable mods) pkgs;
 
   isAvailable = _: mod:
-  if isNull build then
+  if (build == null) then
     true
   else if build.isTiles then
     mod.forTiles or false
diff --git a/pkgs/games/curseofwar/default.nix b/pkgs/games/curseofwar/default.nix
index 6271a60f5b9c..fef456816ff2 100644
--- a/pkgs/games/curseofwar/default.nix
+++ b/pkgs/games/curseofwar/default.nix
@@ -20,7 +20,7 @@ stdenv.mkDerivation rec {
     SDL
   ];
 
-  makeFlags = (if isNull SDL then [] else [ "SDL=yes" ]) ++ [
+  makeFlags = (lib.optionals (SDL != null) [ "SDL=yes" ]) ++ [
     "PREFIX=$(out)"
     # force platform's cc on darwin, otherwise gcc is used
     "CC=${stdenv.cc.targetPrefix}cc"
diff --git a/pkgs/servers/nosql/arangodb/default.nix b/pkgs/servers/nosql/arangodb/default.nix
index 3d15654300ca..443fdeffb10a 100644
--- a/pkgs/servers/nosql/arangodb/default.nix
+++ b/pkgs/servers/nosql/arangodb/default.nix
@@ -25,7 +25,7 @@ let
     else "core";
 
   targetArch =
-    if isNull targetArchitecture
+    if targetArchitecture == null
     then defaultTargetArchitecture
     else targetArchitecture;
 in
diff --git a/pkgs/stdenv/generic/make-derivation.nix b/pkgs/stdenv/generic/make-derivation.nix
index 6bf319d07308..890cf4b668d7 100644
--- a/pkgs/stdenv/generic/make-derivation.nix
+++ b/pkgs/stdenv/generic/make-derivation.nix
@@ -206,7 +206,7 @@ let
 
   checkDependencyList = checkDependencyList' [];
   checkDependencyList' = positions: name: deps: lib.flip lib.imap1 deps (index: dep:
-    if lib.isDerivation dep || isNull dep || builtins.typeOf dep == "string" || builtins.typeOf dep == "path" then dep
+    if lib.isDerivation dep || dep == null || builtins.typeOf dep == "string" || builtins.typeOf dep == "path" then dep
     else if lib.isList dep then checkDependencyList' ([index] ++ positions) name dep
     else throw "Dependency is not of a valid type: ${lib.concatMapStrings (ix: "element ${toString ix} of ") ([index] ++ positions)}${name} for ${attrs.name or attrs.pname}");
 in if builtins.length erroneousHardeningFlags != 0
diff --git a/pkgs/tools/misc/plfit/default.nix b/pkgs/tools/misc/plfit/default.nix
index 60d08e69d457..78e7c3572b6f 100644
--- a/pkgs/tools/misc/plfit/default.nix
+++ b/pkgs/tools/misc/plfit/default.nix
@@ -20,14 +20,14 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [
     cmake
-  ] ++ lib.optionals (!isNull python) [
+  ] ++ lib.optionals (python != null) [
     python
     swig
   ];
 
   cmakeFlags = [
     "-DPLFIT_USE_OPENMP=ON"
-  ] ++ lib.optionals (!isNull python) [
+  ] ++ lib.optionals (python != null) [
     "-DPLFIT_COMPILE_PYTHON_MODULE=ON"
   ];
 
diff --git a/pkgs/tools/text/gawk/gawkextlib.nix b/pkgs/tools/text/gawk/gawkextlib.nix
index d15d5ce75f41..e050c9939269 100644
--- a/pkgs/tools/text/gawk/gawkextlib.nix
+++ b/pkgs/tools/text/gawk/gawkextlib.nix
@@ -6,7 +6,7 @@
 let
   buildExtension = lib.makeOverridable
     ({ name, gawkextlib, extraBuildInputs ? [ ], doCheck ? true }:
-      let is_extension = !isNull gawkextlib;
+      let is_extension = gawkextlib != null;
       in stdenv.mkDerivation rec {
         pname = "gawkextlib-${name}";
         version = "unstable-2019-11-21";