diff -r 31c61b6dcaa5 -r dc88d2ece7e4 src/hash_map.c
--- a/src/hash_map.c	Fri Aug 15 17:46:47 2025 +0200
+++ b/src/hash_map.c	Sun Aug 17 23:05:16 2025 +0200
@@ -78,7 +78,7 @@
     cxFree(map->collection.allocator, map);
 }
 
-static int cx_hash_map_put(
+static void *cx_hash_map_put(
         CxMap *map,
         CxHashKey key,
         void *value
@@ -105,7 +105,9 @@
         memcmp(elm->key.data, key.data, key.len) == 0) {
         // overwrite existing element, but call destructors first
         cx_invoke_destructor(map, elm->data);
-        if (map->collection.store_pointer) {
+        if (value == NULL) {
+            memset(elm->data, 0, map->collection.elem_size);
+        } else if (map->collection.store_pointer) {
             memcpy(elm->data, &value, sizeof(void *));
         } else {
             memcpy(elm->data, value, map->collection.elem_size);
@@ -116,10 +118,12 @@
                 allocator,
                 sizeof(struct cx_hash_map_element_s) + map->collection.elem_size
         );
-        if (e == NULL) return -1;
+        if (e == NULL) return NULL;
 
         // write the value
-        if (map->collection.store_pointer) {
+        if (value == NULL) {
+            memset(e->data, 0, map->collection.elem_size);
+        } else if (map->collection.store_pointer) {
             memcpy(e->data, &value, sizeof(void *));
         } else {
             memcpy(e->data, value, map->collection.elem_size);
@@ -127,7 +131,10 @@
 
         // copy the key
         void *kd = cxMalloc(allocator, key.len);
-        if (kd == NULL) return -1;
+        if (kd == NULL) {
+            cxFree(allocator, e);
+            return NULL;
+        }
         memcpy(kd, key.data, key.len);
         e->key.data = kd;
         e->key.len = key.len;
@@ -140,12 +147,14 @@
             prev->next = e;
         }
         e->next = elm;
+        elm = e;
 
         // increase the size
         map->collection.size++;
     }
 
-    return 0;
+    // return pointer to the element
+    return elm->data;
 }
 
 static void cx_hash_map_unlink(