Fix for bug #32557: order by updatexml causes assertion in filesort

Problem: even if an Item_xml_str_func successor returns NULL, it doesn't have 
a corresponding property (maybe_null) set, that leads to a failed assertion.

Fix: set nullability property of Item_xml_str_func.


mysql-test/r/xml.result:
  Fix for bug #32557: order by updatexml causes assertion in filesort
    - test result.
mysql-test/t/xml.test:
  Fix for bug #32557: order by updatexml causes assertion in filesort
    - test case.
sql/item_xmlfunc.h:
  Fix for bug #32557: order by updatexml causes assertion in filesort
    - set Item_xml_str_func::maybe_null.

1 files changed, 10 insertions, 2 deletions

diff --git a/sql/item_xmlfunc.h b/sql/item_xmlfunc.h
index 278c98baf7c..dadbb5ccf42 100644
--- a/sql/item_xmlfunc.h
+++ b/sql/item_xmlfunc.h
@@ -28,8 +28,16 @@ protected:
   String tmp_value, pxml;
   Item *nodeset_func;
 public:
-  Item_xml_str_func(Item *a, Item *b): Item_str_func(a,b) {}
-  Item_xml_str_func(Item *a, Item *b, Item *c): Item_str_func(a,b,c) {}
+  Item_xml_str_func(Item *a, Item *b): 
+    Item_str_func(a,b) 
+  {
+    maybe_null= TRUE;
+  }
+  Item_xml_str_func(Item *a, Item *b, Item *c): 
+    Item_str_func(a,b,c) 
+  {
+    maybe_null= TRUE;
+  }
   void fix_length_and_dec();
   String *parse_xml(String *raw_xml, String *parsed_xml_buf);
 };