BUG#36139 "float, zerofill, crash with subquery"

- Make convert_zerofill_number_to_string() take into account that the 
  constant it is converting may evaluate to NULL.


mysql-test/r/subselect.result:
  BUG#36139 "float, zerofill, crash with subquery"
  - Testcase
mysql-test/t/subselect.test:
  BUG#36139 "float, zerofill, crash with subquery"
  - Testcase

1 files changed, 8 insertions, 3 deletions

diff --git a/sql/item.cc b/sql/item.cc
index 553ba1b152c..9ff1f8c0084 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -4156,9 +4156,14 @@ static void convert_zerofill_number_to_string(Item **item, Field_num *field)
   String tmp(buff,sizeof(buff), field->charset()), *res;
 
   res= (*item)->val_str(&tmp);
-  field->prepend_zeros(res);
-  pos= (char *) sql_strmake (res->ptr(), res->length());
-  *item= new Item_string(pos, res->length(), field->charset());
+  if ((*item)->is_null())
+    *item= new Item_null();
+  else
+  {
+    field->prepend_zeros(res);
+    pos= (char *) sql_strmake (res->ptr(), res->length());
+    *item= new Item_string(pos, res->length(), field->charset());
+  }
 }