Avoid the possibility of returning a typed nil.
Merge pull request #390 from howbazaar/fix-explosion

Avoid the possibility of returning a typed nil.

The test asserts "gc.IsNil", unfortunately this let a typed nil through.

The caller of this was doing "if info != nil", the typed nil is != nil, so it blew up on the second part.

We can't change the test for this until we write jc.IsNil that asserts a nil interface if the result is an interface, rather than just the value part of the interface.