diff -r d938228c382e -r e2093ca0ef90 src/ucx/cx/hash_key.h
--- a/src/ucx/cx/hash_key.h	Sun Nov 06 15:53:32 2022 +0100
+++ b/src/ucx/cx/hash_key.h	Sun Nov 06 16:59:39 2022 +0100
@@ -50,9 +50,10 @@
     union {
         unsigned char *bytes;
         unsigned char const *cbytes;
+        char *str;
         char const *cstr;
-        char *str;
         void *obj;
+        void const *cobj;
     } data;
     /**
      * The key data length.
@@ -68,11 +69,13 @@
 typedef struct cx_hash_key_s CxHashKey;
 
 /**
- * Computes a murmur hash-2.
+ * Computes a murmur2 32 bit hash.
  *
- * You need to initialize data and len in the key struct.
+ * You need to initialize \c data and \c len in the key struct.
  * The hash is then directly written to that struct.
  *
+ * \note If \c data is \c NULL, the hash is defined as 1574210520.
+ *
  * @param key the key, the hash shall be computed for
  */
 void cx_hash_murmur(CxHashKey *key);
@@ -114,7 +117,7 @@
  */
 __attribute__((__warn_unused_result__))
 CxHashKey cx_hash_key(
-        void *obj,
+        void const *obj,
         size_t len
 );