diff -rup libid3tag-0.16.1.orig/ucs4.c libid3tag-0.16.1/ucs4.c
--- libid3tag-0.16.1.orig/ucs4.c	2021-08-15 22:52:07.000000000 +0200
+++ libid3tag-0.16.1/ucs4.c	2022-04-08 09:47:54.980481313 +0200
@@ -39,6 +39,9 @@ id3_length_t id3_ucs4_length(id3_ucs4_t
 {
   id3_ucs4_t const *ptr = ucs4;
 
+  if (! ucs4)
+    return 0;
+
   while (*ptr)
     ++ptr;