MultipleObjectsReturned on GTIN search

[Jongmassey]

via this sentry entry and this slack thread - when there are multiple AMPPs for a given GTIN, a MultipleObjectsReturned error is thrown

[Jongmassey]

Digging into this using google bigquery - it seems that there are duplicate records based on GTIN in dmd.gtin. Therefore, when searching for AMPPs by GTIN, a query may return multiple AMPPs, which violates the expected behaviour of .get() to return only one item.

For some of these duplicates, only one of the duplicated rows has a NULL enddt - so when searching for the current GTIN info then there would be no duplicates. However, for some GTINs there are multiple rows with NULL enddts.

The test fixtures and probably some of the tests will need updating to account for this, as they do not currently reflect this duplication.