Allow null element in list (#271)

bubbleUpNullValuesInPlaceRec was incorrectly marking a nil as an error
and attempting to bubble up errors to the next field in places where a
null object was acceptable.

execution_result.go

@@ -287,6 +287,11 @@ func bubbleUpNullValuesInPlaceRec(schema *ast.Schema, currentType *ast.Type, sel
 			}
 			errs = append(errs, lowerErrs...)
 		}
+	case nil:
+		if currentType.Elem.NonNull {
+			return nil, false, fmt.Errorf("bubbleUpNullValuesInPlaceRec: unxpected result type '%T'", result)
+		}
+		return
 	default:
 		return nil, false, fmt.Errorf("bubbleUpNullValuesInPlaceRec: unxpected result type '%T'", result)
 	}

execution_result_test.go

@@ -1171,6 +1171,80 @@ func TestBubbleUpNullValuesInPlace(t *testing.T) {
 			}}), errs)
 		require.Equal(t, jsonToInterfaceMap(`{ "critters": [ { "id": "GIZMO1", "color": "RED", "_bramble__typename": "Gizmo"  }, { "id": "GREMLIN1", "name": "Spikey", "_bramble__typename": "Gremlin" }, null ]	}`), result)
 	})
+
+	t.Run("works with nullable null in array", func(t *testing.T) {
+		ddl := `
+		type Gizmo {
+			id: ID!
+			color: String!
+		}
+
+		type Query {
+			gizmos: [Gizmo]!
+		}`
+
+		result := jsonToInterfaceMap(`
+			{
+				"gizmos": [
+					{ "id": "GIZMO1", "color": "RED" },
+					null,
+					{ "id": "GIZMO2", "color": "GREEN" }
+				]
+			}
+		`)
+
+		schema := gqlparser.MustLoadSchema(&ast.Source{Name: "fixture", Input: ddl})
+
+		query := `
+			{
+				gizmos {
+					id
+					color
+				}
+			}`
+
+		document := gqlparser.MustLoadQuery(schema, query)
+		errs, err := bubbleUpNullValuesInPlace(schema, document.Operations[0].SelectionSet, result)
+		require.NoError(t, err)
+		require.Equal(t, []*gqlerror.Error(nil), errs)
+		require.Equal(t, jsonToInterfaceMap(`{ "gizmos": [ { "id": "GIZMO1", "color": "RED" }, null, { "id": "GIZMO2", "color": "GREEN" } ]	}`), result)
+	})
+	t.Run("works with not nullable null in array", func(t *testing.T) {
+		ddl := `
+		type Gizmo {
+			id: ID!
+			color: String!
+		}
+
+		type Query {
+			gizmos: [Gizmo!]!
+		}`
+
+		result := jsonToInterfaceMap(`
+			{
+				"gizmos": [
+					{ "id": "GIZMO1", "color": "RED" },
+					null,
+					{ "id": "GIZMO2", "color": "GREEN" }
+				]
+			}
+		`)
+
+		schema := gqlparser.MustLoadSchema(&ast.Source{Name: "fixture", Input: ddl})
+
+		query := `
+			{
+				gizmos {
+					id
+					color
+				}
+			}`
+
+		document := gqlparser.MustLoadQuery(schema, query)
+		errs, err := bubbleUpNullValuesInPlace(schema, document.Operations[0].SelectionSet, result)
+		require.Error(t, err)
+		require.Equal(t, []*gqlerror.Error(nil), errs)
+	})
 }
 
 func TestFormatResponseBody(t *testing.T) {