Nested Aggregation Usageedit

a => a
.Nested("tags", n => n
    .Path(p => p.Tags)
    .Aggregations(aa => aa
        .Terms("tag_names", t => t
            .Field(p => p.Tags.Suffix("name"))
        )
    )
)
new NestedAggregation("tags")
{
    Path = "tags",
    Aggregations = new TermsAggregation("tag_names")
    {
        Field = "tags.name"
    }
}

Example json output. 

{
  "tags": {
    "nested": {
      "path": "tags"
    },
    "aggs": {
      "tag_names": {
        "terms": {
          "field": "tags.name"
        }
      }
    }
  }
}

Handling Responsesedit

response.ShouldBeValid();
var tags = response.Aggregations.Nested("tags");
tags.Should().NotBeNull();
var tagNames = tags.Terms("tag_names");
tagNames.Should().NotBeNull();
foreach(var item in tagNames.Buckets)
{
    item.Key.Should().NotBeNullOrEmpty();
    item.DocCount.Should().BeGreaterThan(0);
}