Introduce `mapNullable` into lib and use it in a few places

Also simply some configure flag logic my grep also alerted me too.

2 files changed, 2 insertions, 2 deletions

diff --git a/nixos/modules/services/monitoring/graphite.nix b/nixos/modules/services/monitoring/graphite.nix
index c5352e5887da..98931e65bb56 100644
--- a/nixos/modules/services/monitoring/graphite.nix
+++ b/nixos/modules/services/monitoring/graphite.nix
@@ -4,7 +4,7 @@ with lib;
 
 let
   cfg = config.services.graphite;
-  writeTextOrNull = f: t: if t == null then null else pkgs.writeTextDir f t;
+  writeTextOrNull = f: t: mapNullable (pkgs.writeTextDir f) t;
 
   dataDir = cfg.dataDir;
 
diff --git a/nixos/modules/services/monitoring/prometheus/default.nix b/nixos/modules/services/monitoring/prometheus/default.nix
index cf9deccbffe2..5c4a48a7db4b 100644
--- a/nixos/modules/services/monitoring/prometheus/default.nix
+++ b/nixos/modules/services/monitoring/prometheus/default.nix
@@ -134,7 +134,7 @@ let
           };
         });
         default = null;
-        apply = x: if x == null then null else _filter x;
+        apply = x: mapNullable _filter x;
         description = ''
           Optional http login credentials for metrics scraping.
         '';