Fix internal server error when providing an association as the filter param

[unnawut]

Issue/Task Number: #1051

Overview

This PR fixes a specific case of filtering when an association name is given as the filter param without specifying the association's field.

Changes

• Add a guard so association filters do not get processed as a field.

Implementation Details

Overlay filters could be in the form of:

[
  some_field: nil,
  some_id: :uuid,
  some_assoc: [:id, :name]
]

So when an association is given as a filter param without its dot-notated subfield, e.g. field: "some_assoc" instead of field: "some_assoc.id", it treats [:id, :name] as a field type like :uuid instead of a list of associated subfields, and hence the internal server error.

An is_list(type) guard is added to catch the association and return : missing_subfield for further processing by the parser and orchestrator.

Usage

Try the request in #1051. Its return should be similar to:

{
  "version": "1",
  "success": false,
  "data": {
    "object": "error",
    "messages": null,
    "description": "Invalid parameter provided. The queried field must refer to the object's field, not the object. Given: 'from_wallet'.",
    "code": "client:invalid_parameter"
  }
}

Impact

No changes to the API specs or DB schema.