fix String method on the OptionalString

Author: marten-seemann

types.go

@@ -358,9 +358,9 @@ func (p *OptionalString) UnmarshalJSON(input []byte) error {
 
 func (p OptionalString) String() string {
 	if p.value == nil {
-		return "default"
+		return ""
 	}
-	return fmt.Sprintf("%d", p.value)
+	return *p.value
 }
 
 var _ json.Unmarshaler = (*OptionalInteger)(nil)

types_test.go

@@ -407,11 +407,13 @@ func TestOptionalString(t *testing.T) {
 		t.Fatal("should be the default")
 	}
 	if val := defaultOptionalString.WithDefault(""); val != "" {
-		t.Errorf("optional integer should have been empty, got %s", val)
+		t.Errorf("optional string should have been empty, got %s", val)
+	}
+	if val := defaultOptionalString.String(); val != "" {
+		t.Fatalf("default optional string should be an empty string, got %s", val)
 	}
-
 	if val := defaultOptionalString.WithDefault("foo"); val != "foo" {
-		t.Errorf("optional integer should have been foo, got %s", val)
+		t.Errorf("optional string should have been foo, got %s", val)
 	}
 
 	var filledStr OptionalString
@@ -420,12 +422,14 @@ func TestOptionalString(t *testing.T) {
 		t.Fatal("should not be the default")
 	}
 	if val := filledStr.WithDefault("bar"); val != "foo" {
-		t.Errorf("optional integer should have been foo, got %s", val)
+		t.Errorf("optional string should have been foo, got %s", val)
+	}
+	if val := filledStr.String(); val != "foo" {
+		t.Fatalf("optional string should have been foo, got %s", val)
 	}
-
 	filledStr = OptionalString{value: makeStringPointer("")}
 	if val := filledStr.WithDefault("foo"); val != "" {
-		t.Errorf("optional integer should have been 0, got %s", val)
+		t.Errorf("optional string should have been 0, got %s", val)
 	}
 
 	for jsonStr, goValue := range map[string]OptionalString{