MDEV-33659 Fix crash in kdf() without parameters

mysql-test/main/func_kdf.result

@@ -154,5 +154,10 @@ NULL
 Warnings:
 Warning	3047	Invalid argument error: 65537 in function kdf.
 #
+# MDEV-33659 Test kdf() without parameters
+#
+select kdf();
+ERROR 42000: Incorrect parameter count in the call to native function 'kdf'
+#
 # End of 11.3 tests
 #

mysql-test/main/func_kdf.test

@@ -51,6 +51,13 @@ select length(kdf('foo', 'bar', 100, 'pbkdf2_hmac', 32768));
 select length(kdf('foo', 'bar', 100, 'pbkdf2_hmac', 65536));
 select length(kdf('foo', 'bar', 100, 'pbkdf2_hmac', 65537));
 
+--echo #
+--echo # MDEV-33659 Test kdf() without parameters
+--echo #
+
+--error ER_WRONG_PARAMCOUNT_TO_NATIVE_FCT
+select kdf();
+
 --echo #
 --echo # End of 11.3 tests
 --echo #

sql/item_create.cc

@@ -3229,8 +3229,12 @@ Item*
 Create_func_kdf::create_native(THD *thd, const LEX_CSTRING *name,
                                List<Item> *item_list)
 {
-  uint arg_count= item_list->elements;
   Item *a[5];
+  uint arg_count= 0;
+
+  if (item_list != NULL)
+    arg_count= item_list->elements;
+
   for (uint i=0; i < MY_MIN(array_elements(a), arg_count); i++)
     a[i]= item_list->pop();
   switch (arg_count)