A fix for the bug with:

delete from table where column<=>NULL 
on indexed columns

mysql-test/r/delete.result

@@ -24,3 +24,9 @@ create table t1 (a bigint not null, primary key (a,a,a,a,a,a,a,a,a,a));
 insert into t1 values (2),(4),(6),(8),(10),(12),(14),(16),(18),(20),(22),(24),(26),(23),(27);
 delete from t1 where a=27;
 drop table t1;
+create table t1 (id int, index(id));
+insert into t1 values(NULL);
+delete from t1 where id <=> NULL;
+select * from t1;
+id
+drop table if exists t1;

mysql-test/t/delete.test

@@ -35,3 +35,8 @@ create table t1 (a bigint not null, primary key (a,a,a,a,a,a,a,a,a,a));
 insert into t1 values (2),(4),(6),(8),(10),(12),(14),(16),(18),(20),(22),(24),(26),(23),(27);
 delete from t1 where a=27;
 drop table t1;
+create table t1 (id int, index(id));
+insert into t1 values(NULL);
+delete from t1 where id <=> NULL;
+select * from t1;
+drop table if exists t1;

sql/opt_range.cc

@@ -1024,7 +1024,7 @@ get_mm_leaf(PARAM *param, Field *field, KEY_PART *key_part,
       field->cmp_type() != value->result_type())
     DBUG_RETURN(0);
 
-  if (value->save_in_field(field))
+  if (value->save_in_field(field) || value->is_null())
   {
     // TODO; Check if we can we remove the following block.
     if (type == Item_func::EQUAL_FUNC)