"Cannot return null for non-nullable field" present when error was specified

[virtual-light]

Environment

Elixir 1.9.0 (compiled with Erlang/OTP 22)

absinthe 1.4.16 (Hex package) (mix)
absinthe_relay 1.4.6 (Hex package) (mix)
absinthe_plug 1.4.7 (Hex package) (mix)

Expected behavior

According to current GQL specification paragraph 6.4.4 and working draft of new GQL specification paragraph 6.4.4.

If the field returns null because of an error which has already been added to the "errors" list in the response, the "errors" list must not be further affected. That is, only one error should be added to the errors list per field.

That means, that when non_null field has nil value, but there is already an error related to that field, then "Cannot return null for non-nullable field" error should not be propagated.

For example, if query

field :user, non_null(:user) do
  arg :id, non_null(:id)
  resolve fn args, resolution -> 
   case authorize(args, resolution.context.current_user) do
    :ok
      # next steps
      {:ok, user}
    :error
      {:error, :unauthorized}
  end  
end

returns {:error, :unauthorized} then errors list should contain only one error in response:

%{
  "data" => nil,
  "errors" => [
    %{
      "locations" => [%{"column" => 0, "line" => 2}],
      "message" => "unauthorized",
      "path" => ["user"]
    }
  ]
}

Actual behavior

"Cannot return null for non-nullable field" present in errors list in response.

%{
  "data" => nil,
  "errors" => [
    %{
      "locations" => [%{"column" => 0, "line" => 2}],
      "message" => "Cannot return null for non-nullable field",
      "path" => ["user"]
    },
    %{
      "locations" => [%{"column" => 0, "line" => 2}],
      "message" => "unauthorized",
      "path" => ["user"]
    }
}

[benwilson512]

Ah, it seems they changed the wording on this. Will fix.

[binaryseed]

I put together a small PR to tackle this #816