A Mappings.NoElementException happens on an edge condition for a query using a materialized view.
The query contains a "group by" clause which contains fields from both sides of a join. There is no real reason to group by this same field twice, but there is also no reason that this shouldn't succeed.
Attached is a script which causes this failure. The query causing the problem looks like this:
explain extended select sum(1)
from fact inner join dim1
on fact.f1 = dim1.pk1
group by f1, pk1;