NullReferenceException in AggregationsHelper

[mausch]

Just got a NullReferenceException in https://github.com/elasticsearch/elasticsearch-net/blob/develop/src/Nest/Domain/Aggregations/AggregationsHelper.cs#L127 .
This is because TryGet can return null but then this is never checked anywhere in this class.
IMHO the code should detect the null and throw a specific exception, e.g "Term aggregation XXX not found", what do you think?
Or return null just as many other methods in this class do, like ReverseNested, Nested, etc.