Running nixpkgs-update (https://nix-community.org/update-bot/) with UPDATE_INFO: apacheKafka 0 -> 1
attrpath: apacheKafka
Checking auto update branch...
[version] 
[version] skipping because derivation has updateScript
[rustCrateVersion] 
[rustCrateVersion] No cargoHash found
[golangModuleVersion] 
[golangModuleVersion] Not a buildGoModule package with vendorHash
[npmDepsVersion] 
[npmDepsVersion] No npmDepsHash
[updateScript] 
[updateScript] Success
[updateScript] this derivation will be built:
  /nix/store/iamsn6hxx1if37jihz834g8vzjippkjg-packages.json.drv
building '/nix/store/iamsn6hxx1if37jihz834g8vzjippkjg-packages.json.drv'...

Going to be running update for following packages:
 - apache-kafka-2.13-4.2.0

Press Enter key to continue...
Running update for:
Enqueuing group of 1 packages
 - apache-kafka-2.13-4.2.0: UPDATING ...
 - apache-kafka-2.13-4.2.0: DONE.

Packages updated!

Diff after rewrites:
diff --git a/pkgs/servers/apache-kafka/4_2.nix b/pkgs/servers/apache-kafka/4_2.nix
index 3bd24b89698f..66a82d08d87d 100644
--- a/pkgs/servers/apache-kafka/4_2.nix
+++ b/pkgs/servers/apache-kafka/4_2.nix
@@ -1,5 +1,5 @@
 import ./generic.nix {
-  kafkaVersion = "4.2.0";
+  kafkaVersion = "4.2.1";
   scalaVersion = "2.13";
-  hash = "sha256-ZklCfC0GKQih+guUHY0idPUlNiAvqhsT41RbOVoihfs=";
+  hash = "sha256-z/g5pZlKj9mwJrVU0JhSgHpu+f1NgkbvFRcyYx2knfo=";
 }

No auto update branch exists
Old version 2.13-4.2.0" not present in master derivation file with contents: import ./generic.nix {
  kafkaVersion = "4.2.0";
  scalaVersion = "2.13";
  hash = "sha256-ZklCfC0GKQih+guUHY0idPUlNiAvqhsT41RbOVoihfs=";
}