Merge rkalimullin@bk-internal.mysql.com:/home/bk/mysql-5.1-maint

into  mysql.com:/usr/home/ram/work/bug23254/my51-bug23254

mysql-test/r/func_compress.result

@@ -79,6 +79,16 @@ uncompress(a)	uncompressed_length(a)
 NULL	NULL
 a	1
 drop table t1;
+create table t1(a blob);
+insert into t1 values ('0'), (NULL), ('0');
+select compress(a), compress(a) from t1;
+select compress(a) is null from t1;
+compress(a) is null
+0
+1
+0
+drop table t1;
+End of 4.1 tests
 create table t1 (a varchar(32) not null);
 insert into t1 values ('foo');
 explain select * from t1 where uncompress(a) is null;

mysql-test/t/func_compress.test

@@ -56,7 +56,19 @@ insert into t1 values(NULL), (compress('a'));
 select uncompress(a), uncompressed_length(a) from t1;
 drop table t1;
 
-# End of 4.1 tests
+#
+# Bug #23254: problem with compress(NULL)
+#
+
+create table t1(a blob);
+insert into t1 values ('0'), (NULL), ('0');
+--disable_result_log
+select compress(a), compress(a) from t1;
+--enable_result_log
+select compress(a) is null from t1;
+drop table t1;
+
+--echo End of 4.1 tests
 
 #
 # Bug #18539: uncompress(d) is null: impossible?

sql/item_strfunc.cc

@@ -2965,6 +2965,7 @@ String *Item_func_compress::val_str(String *str)
     null_value= 1;
     return 0;
   }
+  null_value= 0;
   if (res->is_empty()) return res;
 
   /*