update changelog

CHANGELOG.md

@@ -4,6 +4,7 @@ All notable changes to Pantools will be documented in this file.
 
 ### Fixed
 - Clearer error message for homology group identifiers that could not by found by `group_info` (!253).
+- Prevent NullPointerException in `gene_classification` (!254).
 
 ## [4.3.2] - 20-12-2024