Assert failure in ATPrepAddPrimaryKey

I ran into an Assert failure in ATPrepAddPrimaryKey() with the query
below:

CREATE TABLE t0(c0 boolean);
CREATE TABLE t1() INHERITS(t0);

# ALTER TABLE t0 ADD CONSTRAINT m EXCLUDE ((1) WITH =);
server closed the connection unexpectedly

The related codes are

    foreach(lc, stmt->indexParams)
    {
        IndexElem  *elem = lfirst_node(IndexElem, lc);
        Constraint *nnconstr;

        Assert(elem->expr == NULL);

It seems to be introduced by b0e96f3119.

Thanks
Richard