backport #41437, commit 62803

mysql-test/r/mysql.result

@@ -180,4 +180,6 @@ ERROR at line 1: DELIMITER cannot contain a backslash character
 1
 This is a file starting with UTF8 BOM 0xEFBBBF
 This is a file starting with UTF8 BOM 0xEFBBBF
+@z:='1'	@z=database()
+1	NULL
 End of 5.0 tests

mysql-test/t/mysql.test

@@ -290,4 +290,9 @@ EOF
 --exec $MYSQL < $MYSQLTEST_VARDIR/tmp/bug29323.sql 2>&1
 remove_file $MYSQLTEST_VARDIR/tmp/bug29323.sql;
 
+#
+# Bug #41437: Value stored in 'case' lacks charset, causees segfault
+#
+--exec $MYSQL -e "select @z:='1',@z=database()"
+
 --echo End of 5.0 tests

sql/item_strfunc.cc

@@ -1696,6 +1696,12 @@ Item *Item_func_sysconst::safe_charset_converter(CHARSET_INFO *tocs)
   Item_string *conv;
   uint conv_errors;
   String tmp, cstr, *ostr= val_str(&tmp);
+  if (null_value)
+  {
+    Item *null_item= new Item_null((char *) fully_qualified_func_name());
+    null_item->collation.set (tocs);
+    return null_item;
+  }
   cstr.copy(ostr->ptr(), ostr->length(), ostr->charset(), tocs, &conv_errors);
   if (conv_errors ||
       !(conv= new Item_static_string_func(fully_qualified_func_name(),