MFH: fix #43559 (array_merge_recursive() doesn't behave as expected with duplicate NULL values)

patch by Felipe

ext/standard/array.c

@@ -2197,8 +2197,18 @@ PHPAPI int php_array_merge(HashTable *dest, HashTable *src, int recursive TSRMLS
 					SEPARATE_ZVAL(dest_entry);
 					SEPARATE_ZVAL(src_entry);
 
-					convert_to_array_ex(dest_entry);
-					convert_to_array_ex(src_entry);
+					if (Z_TYPE_PP(dest_entry) == IS_NULL) {
+						convert_to_array_ex(dest_entry);
+						add_next_index_null(*dest_entry);
+					} else {
+						convert_to_array_ex(dest_entry);
+					}
+					if (Z_TYPE_PP(src_entry) == IS_NULL) {
+						convert_to_array_ex(src_entry);
+						add_next_index_null(*src_entry);
+					} else {
+						convert_to_array_ex(src_entry);
+					}
 					if (thash) {
 						thash->nApplyCount++;
 					}

ext/standard/tests/array/array_merge_recursive_variation5.phpt

@@ -374,8 +374,10 @@ array(8) {
   object(classA)#%d (0) {
   }
   ["string"]=>
-  array(1) {
+  array(2) {
     [0]=>
+    NULL
+    [1]=>
     string(5) "hello"
   }
   ["resource"]=>