NPE on a query with having clause involving a join

A simple query involving a join and having clause causes a NPE. Any subsequent executions cause severe errors. It almost looks like the underlying connection was closed out.

====

C:\apps\derby\db-derby-10.4.2.0-bin\db-derby-10.4.2.0-bin\bin>ij
ij version 10.4
ij> connect 'jdbc:derby://speed:1527/ClassicModels;user=sa;password=sa
';
ij> create table t1(i int, c varchar(20));
0 rows inserted/updated/deleted
ij> create table t2(i int, c2 varchar(20), i2 int);
0 rows inserted/updated/deleted
ij> insert into t1 values(1, 'abc');
1 row inserted/updated/deleted
ij> insert into t1 values(2, 'abc');
1 row inserted/updated/deleted
ij> insert into t2 values(1, 'xyz', 10);
1 row inserted/updated/deleted
ij> insert into t2 values(1, 'aaa', 20);
1 row inserted/updated/deleted
ij> insert into t2 values(2, 'xxx', 30);
1 row inserted/updated/deleted
ij> select t1.i, avg(t2.i2) from t1 inner join t2 on (t1.i = t2.i) group by t1.i
having avg(t2.i2) > 0;
ERROR XJ001: DERBY SQL error: SQLCODE: -1, SQLSTATE: XJ001, SQLERRMC: java.lang.
NullPointerException¶¶XJ001.U