Merge fix for BUG#6976 from 4.0

mysql-test/r/group_by.result

@@ -638,3 +638,15 @@ alias
 1,2
 1
 drop table t1;
+create table t1 (a int);
+insert into t1 values(null);
+select min(a) is null from t1;
+min(a) is null
+1
+select min(a) is null or null from t1;
+min(a) is null or null
+1
+select 1 and min(a) is null from t1;
+1 and min(a) is null
+1
+drop table t1;

mysql-test/t/group_by.test

@@ -465,3 +465,12 @@ select group_concat( distinct col1 ) as alias from t1
 
 drop table t1;
 
+
+#Test for BUG#6976: Aggregate functions have incorrect NULL-ness
+create table t1 (a int);
+insert into t1 values(null);
+select min(a) is null from t1;
+select min(a) is null or null from t1;
+select 1 and min(a) is null from t1;
+drop table t1;
+