Retrieving JSON arrays via fields selector is broken in Ditto 3.5.1

[AkshayKumarCB]

The GET /api/2/search/things API is currently broken on the release Ditto 3.5.1 when we attempt to fetch an array property.
A sample scenario is given below.

Sample data stored in Ditto:

{
  "thingId": "sample.eclipse.com:test_1",
  "policyId": "sample.eclipse.com:policy-default",
  "attributes": {
    "a": "b"
  },
  "features": {
    "values": {
      "properties": {
        "a": [
          1,
          2,
          3
        ]
      }
    }
  }
}

API query to fetch only the array 'a' from the Ditto thing:
/api/2/search/things?namespaces=sample.eclipse.com&fields=features/values/properties/a

Response on Ditto 3.4.4: (Returns array with values for "a")
{"items":[{"features":{"values":{"properties":{"a":[1,2,3]}}}}],"nextPageOffset":-1}

Response on Ditto 3.5.1: (Returns an empty array for "a")
{"items":[{"features": { "values": { "properties": { "a": [] }}}}],"nextPageOffset": -1}

However, if we were to update the fields query parameter in the request from features/values/properties/a to features/values/properties, we get the correct response - similar to what was observed in 3.4.4.

Looks like we have a bug for search/things API for arrays in 3.5.1 that needs to be fixed.

Reproducibility rate: 100% (5/5)

[AkshayKumarCB]

Looks like the same behavior is also observed for /api/2/things API:

Request: /api/2/things/sample.eclipse.com:test_1?fields=features/values/properties/a
Response: {"features":{"values":{"properties":{"a":[]}}}}

Request: /api/2/things/sample.eclipse.com:test_1?fields=features/values/properties
Respnose: {"features":{"values":{"properties":{"a":[1,2,3]}}}}

[thjaeckle]

Thanks a lot @AkshayKumarCB for the bugreport.
I will look into it - I remember having changed something around the field selection.

[thjaeckle]

I assume this bug was introduced in PR #1860