Update changelog

Author: brophdawg11

.changeset/proud-timers-tickle.md

@@ -2,4 +2,5 @@
 "@remix-run/router": patch
 ---
 
-fix: actions/loaders returning undefined should throw an error
+- Throw an error if an `action`/`loader` function returns `undefined` as revalidations need to know whether the loader has previously been executed. `undefined` also causes issues during SSR stringification for hydration. You should always ensure you loader/acton return a value, and you may return `null` if you don't wish to return anything.
+- Enhanced `ErrorResponse` bodies to contain more descriptive text in internal 403/404/405 scenarios