elasticsearch-nest-error.md

NEST version: 1.5.0

System.ArgumentException: An item with the same key has already been added.
  at System.ThrowHelper.ThrowArgumentException (ExceptionResource resource) <0x4151e330 + 0x00039> in <filename unknown>:0 
  at System.Collections.Generic.Dictionary`2[TKey,TValue].Insert (System.Collections.Generic.TKey key, System.Collections.Generic.TValue value, Boolean add) <0x41101000 + 0x0019b> in <filename unknown>:0 
  at System.Collections.Generic.Dictionary`2[TKey,TValue].Add (System.Collections.Generic.TKey key, System.Collections.Generic.TValue value) <0x4114c880 + 0x00023> in <filename unknown>:0 
  at System.Collections.ObjectModel.KeyedCollection`2[TKey,TItem].AddKey (System.Collections.ObjectModel.TKey key, System.Collections.ObjectModel.TItem item) <0x414b62f0 + 0x00045> in <filename unknown>:0 
  at System.Collections.ObjectModel.KeyedCollection`2[TKey,TItem].InsertItem (Int32 index, System.Collections.ObjectModel.TItem item) <0x414b6240 + 0x0004b> in <filename unknown>:0 
  at System.Collections.ObjectModel.Collection`1[T].Add (System.Collections.ObjectModel.T item) <0x412408f0 + 0x000ad> in <filename unknown>:0 
  at Newtonsoft.Json.Utilities.CollectionUtils.AddRange[T] (IList`1 initial, IEnumerable`1 collection) <0x414b1280 + 0x000b3> in <filename unknown>:0 
  at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateObjectContract (System.Type objectType) <0x414a9e90 + 0x000ec> in <filename unknown>:0 
  at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateContract (System.Type objectType) <0x414a4bd0 + 0x000ad> in <filename unknown>:0 
  at Nest.Resolvers.ElasticContractResolver.CreateContract (System.Type objectType) <0x415192d0 + 0x00038> in <filename unknown>:0 
  at Newtonsoft.Json.Serialization.DefaultContractResolver.ResolveContract (System.Type type) <0x414a4790 + 0x00149> in <filename unknown>:0 
  at Nest.Resolvers.SettingsContractResolver.ResolveContract (System.Type type) <0x415192a0 + 0x0002a> in <filename unknown>:0 
  at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.GetContractSafe (System.Object value) <0x414a4740 + 0x0003e> in <filename unknown>:0 
  at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize (Newtonsoft.Json.JsonWriter jsonWriter, System.Object value, System.Type objectType) <0x414a4470 + 0x0009f> in <filename unknown>:0 
  at Newtonsoft.Json.JsonSerializer.SerializeInternal (Newtonsoft.Json.JsonWriter jsonWriter, System.Object value, System.Type objectType) <0x414a3940 + 0x005b1> in <filename unknown>:0 
  at Newtonsoft.Json.JsonSerializer.Serialize (Newtonsoft.Json.JsonWriter jsonWriter, System.Object value, System.Type objectType) <0x41519270 + 0x00020> in <filename unknown>:0 
  at Newtonsoft.Json.JsonConvert.SerializeObjectInternal (System.Object value, System.Type type, Newtonsoft.Json.JsonSerializer jsonSerializer) <0x41518fb0 + 0x00124> in <filename unknown>:0 
  at Newtonsoft.Json.JsonConvert.SerializeObject (System.Object value, System.Type type, Formatting formatting, Newtonsoft.Json.JsonSerializerSettings settings) <0x41518ce0 + 0x00057> in <filename unknown>:0 
  at Newtonsoft.Json.JsonConvert.SerializeObject (System.Object value, Formatting formatting, Newtonsoft.Json.JsonSerializerSettings settings) <0x41518ca0 + 0x0002a> in <filename unknown>:0 
  at Nest.NestSerializer.Serialize (System.Object data, SerializationFormatting formatting) <0x41518c30 + 0x0003b> in <filename unknown>:0 
  at Elasticsearch.Net.Connection.RequestHandlers.RequestHandlerBase.PostData (System.Object data) <0x415188b0 + 0x001e1> in <filename unknown>:0 
  at Elasticsearch.Net.Connection.RequestHandlers.RequestHandlerAsync.RequestAsync[T] (Elasticsearch.Net.Connection.RequestState.TransportRequestState`1 requestState, System.Object data) <0x41518590 + 0x000e4> in <filename unknown>:0 
  at Elasticsearch.Net.Connection.Transport.DoRequestAsync[T] (System.String method, System.String path, System.Object data, IRequestParameters requestParameters) <0x41516a50 + 0x000d0> in <filename unknown>:0 
  at Elasticsearch.Net.ElasticsearchClient.DoRequestAsync[T] (System.String method, System.String path, System.Object data, IRequestParameters requestParameters) <0x415169a0 + 0x0007c> in <filename unknown>:0 
  at Elasticsearch.Net.ElasticsearchClient.SearchAsync[T] (System.String index, System.String type, System.Object body, System.Func`2 requestParameters) <0x41515d10 + 0x0018a> in <filename unknown>:0 
  at Nest.RawDispatch.SearchDispatchAsync[T] (Nest.ElasticsearchPathInfo`1 pathInfo, System.Object body) <0x41514e90 + 0x006b4> in <filename unknown>:0 
  at Nest.ElasticClient.SearchAsync[T,TResult] (System.Func`2 searchSelector) <0x41510ce0 + 0x0014d> in <filename unknown>:0 
  at Nest.ElasticClient.SearchAsync[T] (System.Func`2 searchSelector) <0x41510c80 + 0x0003c> in <filename unknown>:0 

item.cs

[ElasticType(Name = "item")]
public class Item
{
    public string Id { get; set; }

    [ElasticProperty(Index = FieldIndexOption.NotAnalyzed)]
    public string PrimaryId { get; set; }

    [ElasticProperty(Type = FieldType.Nested)]
    public IEnumerable<Bar> Bars { get; set; }

    public IEnumerable<Foo> Foos { get; set; }
}

public class Bar
{
    public string AreaName { get; set; }
}

public class Foo
{
    public string AreaName { get; set; }
}

AreaName is on two unrelated types though so not quite seeing why this would pop up just yet