Aggregations not working when upgrading from 1.3.4 to 1.7.0

Hi guys,

My aggregations, at least some of them, stopped working after I upgraded from version 1.3.4 to version 1.7.0
The mappings are exactly the same and so are the indexed documents.

This simple aggregation doesn't return any results:

"aggs": {
"agg-test": {
"terms": {
"field": ""

Does anyone have a clue about what is happening? I don't see any breaking changes from previous versions to the latest regarding aggregations.