refactor: rename/document chooseFirstNonNilFieldValue

Adds test for nil hasOne polyrelation

Author: brandonc

response.go

@@ -193,7 +193,10 @@ func MarshalOnePayloadEmbedded(w io.Writer, model interface{}) error {
 	return json.NewEncoder(w).Encode(payload)
 }
 
-func chooseFirstNonNilFieldValue(structValue reflect.Value) (reflect.Value, error) {
+// selectChoiceTypeStructField returns the first non-nil struct pointer field in the
+// specified struct value that has a jsonapi type field defined within it.
+// An error is returned if there are no fields matching that definition.
+func selectChoiceTypeStructField(structValue reflect.Value) (reflect.Value, error) {
 	for i := 0; i < structValue.NumField(); i++ {
 		choiceFieldValue := structValue.Field(i)
 		choiceTypeField := choiceFieldValue.Type()
@@ -416,7 +419,7 @@ func visitModelNode(model interface{}, included *map[string]*Node,
 					}
 
 					structValue := choiceValue.Elem()
-					if found, err := chooseFirstNonNilFieldValue(structValue); err == nil {
+					if found, err := selectChoiceTypeStructField(structValue); err == nil {
 						fieldValue = found
 					}
 				} else {
@@ -442,7 +445,7 @@ func visitModelNode(model interface{}, included *map[string]*Node,
 
 						structValue := itemValue.Elem()
 
-						if found, err := chooseFirstNonNilFieldValue(structValue); err == nil {
+						if found, err := selectChoiceTypeStructField(structValue); err == nil {
 							collection = append(collection, found.Interface())
 						}
 					}

response_test.go

@@ -38,7 +38,7 @@ func TestMarshalPayload(t *testing.T) {
 	}
 }
 
-func TestMarshalPayloadWithOnePolyrelation(t *testing.T) {
+func TestMarshalPayloadWithHasOnePolyrelation(t *testing.T) {
 	blog := &BlogPostWithPoly{
 		ID:    "1",
 		Title: "Hello, World",
@@ -77,7 +77,7 @@ func TestMarshalPayloadWithOnePolyrelation(t *testing.T) {
 	}
 }
 
-func TestMarshalPayloadWithManyPolyrelation(t *testing.T) {
+func TestMarshalPayloadWithHasManyPolyrelation(t *testing.T) {
 	blog := &BlogPostWithPoly{
 		ID:    "1",
 		Title: "Hello, World",
@@ -133,7 +133,7 @@ func TestMarshalPayloadWithManyPolyrelation(t *testing.T) {
 	}
 }
 
-func TestMarshalPayloadWithManyPolyrelationWithNils(t *testing.T) {
+func TestMarshalPayloadWithHasManyPolyrelationWithNils(t *testing.T) {
 	blog := &BlogPostWithPoly{
 		ID:    "1",
 		Title: "Hello, World",
@@ -154,7 +154,20 @@ func TestMarshalPayloadWithManyPolyrelationWithNils(t *testing.T) {
 	}
 }
 
-func TestMarshalPayloadWithManyRelationWithNils(t *testing.T) {
+func TestMarshalPayloadWithHasOneNilPolyrelation(t *testing.T) {
+	blog := &BlogPostWithPoly{
+		ID:    "1",
+		Title: "Hello, World",
+		Hero:  nil,
+	}
+
+	out := bytes.NewBuffer(nil)
+	if err := MarshalPayload(out, blog); err != nil {
+		t.Fatalf("expected no error but got %s", err)
+	}
+}
+
+func TestMarshalPayloadWithHasOneNilRelation(t *testing.T) {
 	blog := &Blog{
 		ID:    1,
 		Title: "Hello, World",