Null object cannot be converted to a value type

[frahugo]

I want to use the API to assign values to recipient tabs in an envelope. So I use something like this:

DocuSign.Api.EnvelopeRecipientTabs.recipients_put_recipient_tabs(connection, account_id, envelope_id, "1", EnvelopeRecipientTabs: newtabs)

newtabs was built using the values returned from DocuSign.Api.EnvelopeRecipientTabs.recipients_get_recipient_tabs/4. Some fields are nil.

When Poison encodes the model, nil value get serialized to null and the DocuSign API does not like it. It returns this error:

   body: "{\r\n  \"errorCode\": \"INVALID_REQUEST_BODY\",\r\n  \"message\": \"The request body is missing or improperly formatted. Null object cannot be converted to a value type.\"\r\n}",

Since this seems to be specific to DocuSign, I was thinking of adding a transformation in RequestBuilder to prune the nil values in a map. This was taken from a closed Posion issue where someone asked for a way to exclude nil values as a feature in Poison( devinus/poison#55).

  @spec add_optional_params(map(), %{optional(atom) => atom}, keyword()) :: map()
  def add_optional_params(request, definitions, [{key, value}] = values) do
    case definitions do
      %{^key => :body} when map_size(definitions) == 1 ->
        # If there is a single entity to send in the body there is no need to
        # enclose it in a multipart request.
        add_param(request, :body, :body, Map.from_struct(value) |> prune_nils())

      _ ->
        do_add_optional_params(request, definitions, values)
    end
  end

  @spec prune_nils(map) :: map
  def prune_nils(s) when is_struct(s), do: s |> Map.from_struct() |> Enum.reduce(%{}, &reducer/2)
  def prune_nils(m) when is_map(m), do: Enum.reduce(m, %{}, &reducer/2)

  @spec reducer({any, any}, map) :: map
  defp reducer({k, v}, map) when is_map(v), do: Map.put(map, k, prune_nils(v))
  defp reducer({_k, v}, map) when is_nil(v), do: map
  defp reducer({k, v}, map), do: Map.put(map, k, v)

Are you OK with this change? I will create a pull request if you are.

[neilberkman]

Yes, this would be great. Thanks!