fix: only null values should also trigger error (#1394)

Co-authored-by: Peter Arentsen <peter.arentsen@bettyblocks.com>

Author: nulian

lib/absinthe/phase/document/validation/one_of_directive.ex

@@ -20,7 +20,7 @@ defmodule Absinthe.Phase.Document.Validation.OneOfDirective do
 
   defp process(%Argument{input_value: %{normalized: %Object{} = object}} = node) do
     if Keyword.has_key?(object.schema_node.__private__, :one_of) and
-         field_count(object.fields) > 1 do
+         field_count(object.fields) != 1 do
       message =
         ~s[The Input Type "#{object.schema_node.name}" has the @oneOf directive. It must have exactly one non-null field.]
 

test/absinthe/phase/document/validation/one_of_directive_test.exs

@@ -57,6 +57,13 @@ defmodule Absinthe.Phase.Document.Validation.OneOfDirectiveTest do
       refute result[:data]
     end
 
+    test "with both inline args nil" do
+      query = ~s[query { valid(input: {id: null, name: null}) }]
+      assert {:ok, %{errors: [error]} = result} = Absinthe.run(query, Schema)
+      assert %{locations: [%{column: 15, line: 1}], message: @message} = error
+      refute result[:data]
+    end
+
     test "with both variable args" do
       options = [variables: %{"input" => %{"id" => 1, "name" => "a"}}]
       assert {:ok, %{errors: [error]} = result} = Absinthe.run(@query, Schema, options)