Deserializing a Common Grams Token Filter that uses a predefined word list fails

[awelburn]

NEST/Elasticsearch.Net version: 5.x
Elasticsearch version: 5.x

Description of the problem including expected versus actual behavior:
Following the examples here: https://www.elastic.co/guide/en/elasticsearch/guide/master/common-grams.html (I know this was written against v2, but I haven't found anything to suggest this filter has changed since?)

Steps to reproduce:

1. Create a new index as per the examples in the url above, using "_english_" as the value for "common_words"
2. Create a nest client and call a method that retrieves index settings, GetIndexAsync() for example.
3. Exception thrown!

Provide DebugInformation (if relevant):
Elasticsearch.Net.UnexpectedElasticsearchClientException: Error converting value "english" to type 'System.Collections.Generic.IEnumerable1[System.String]'. Path 'common_words'. ---> Newtonsoft.Json.JsonSerializationException: Error converting value "_english_" to type 'System.Collections.Generic.IEnumerable1[System.String]'. Path 'common_words'. ---> System.ArgumentException: Could not cast or convert from System.String to System.Collections.Generic.IEnumerable`1[System.String].

[awelburn]

I'm not sure if this is the right attribute to use, but I've fixed the issue locally by adding [JsonConverter(typeof(ReadSingleOrEnumerableJsonConverter<string>))]

to the CommonWords property in ICommonGramsTokenFilter

[russcam]

Thanks for reporting @awelburn. This is a case where NEST only supports an array of values for common_words, so an index created outside of NEST using a single value will cause an exception as seen.

Applying [JsonConverter(typeof(ReadSingleOrEnumerableJsonConverter<string>))] will rectify this. Mind submitting a PR against master with this change?

[russcam]

Closing this. Will be in the next release. Thanks for opening @awelburn 👍