Hard to figure out the bug when an entity for mastering is malformed

[damonfeldman]

I have some content that has "flat" list of properties below the /envelope/instance JSON structure. That is it has

{envelope: {
instance: {
info: {...},
firstName: "bob",
lastName: "jones",
dob: "05-02-1993"
}}

where normally it would/should have a "Person: {...} wrapper around the name, dob, and other data.

It would be nice if this failed more gracefully, rather than throwing a coercion error on a sequence.

Reproduce easily by inserting a second property into the root level of a document and trying to run SMT on it.