Partial success (data + errors) from one service only returns errors

[JohnStarich]

I can reproduce this with a failing test as well:

func TestDataAndErrorsBothReturnFromOneServicePartialSuccess(t *testing.T) {
	schema, err := graphql.LoadSchema(`
type Query {
	foo: String
}
`)
	require.NoError(t, err)
	queryerFactory := QueryerFactory(func(ctx *PlanningContext, url string) graphql.Queryer {
		return graphql.QueryerFunc(func(input *graphql.QueryInput) (interface{}, error) {
			data := map[string]interface{}{"foo": "bar"}
			err := graphql.ErrorList{&graphql.Error{Message: "baz"}}
			return data, err
		})
	})
	gateway, err := New([]*graphql.RemoteSchema{
		{Schema: schema, URL: "boo"},
	}, WithQueryerFactory(&queryerFactory))
	require.NoError(t, err)

	req := httptest.NewRequest(http.MethodPost, "/", strings.NewReader(`{"query": "query { foo }"}`))
	resp := httptest.NewRecorder()
	gateway.GraphQLHandler(resp, req)
	assert.Equal(t, http.StatusOK, resp.Code)
	assert.JSONEq(t, `
		{
			"data": {
				"foo": "bar"
			},
			"errors": [
				{
					"message": "baz",
					"extensions": null
				}
			]
		}
	`, resp.Body.String())
}

Currently fails with:

➜ nautilus-gateway git:(wip/test-missing-data-with-errors) go test . -run TestDataAndErrorsBothReturnFromOneServicePartialSuccess
WARNING Network Error: baz                           
--- FAIL: TestDataAndErrorsBothReturnFromOneServicePartialSuccess (0.00s)
    gateway_test.go:783: 
                Error Trace:    /Users/johnstarich/Documents/IBM/Projects/nautilus-gateway/gateway_test.go:783
                Error:          Not equal: 
                                expected: map[string]interface {}{"data":map[string]interface {}{"foo":"bar"}, "errors":[]interface {}{map[string]interface {}{"extensions":interface {}(nil), "message":"baz"}}}
                                actual  : map[string]interface {}{"data":interface {}(nil), "errors":[]interface {}{map[string]interface {}{"extensions":interface {}(nil), "message":"baz"}}}
                            
                                Diff:
                                --- Expected
                                +++ Actual
                                @@ -1,5 +1,3 @@
                                 (map[string]interface {}) (len=2) {
                                - (string) (len=4) "data": (map[string]interface {}) (len=1) {
                                -  (string) (len=3) "foo": (string) (len=3) "bar"
                                - },
                                + (string) (len=4) "data": (interface {}) <nil>,
                                  (string) (len=6) "errors": ([]interface {}) (len=1) {
                Test:           TestDataAndErrorsBothReturnFromOneServicePartialSuccess
FAIL
FAIL    github.com/nautilus/gateway     3.432s
FAIL
➜ nautilus-gateway git:(wip/test-missing-data-with-errors) 

The GraphQL spec says returning data and errors is expected:
https://spec.graphql.org/October2021/#sec-Response-Format

If the data entry in the response is present (including if it is the value null), the errors entry in the response may contain any field errors that were raised during execution. If field errors were raised during execution, it should contain those errors.