CreatedAt, UpdatedAt are skipped, when toml.Marshal

[snowdream]

Describe the bug

type User struct {
	// Model embeds common database fields (ID, CreatedAt, UpdatedAt, DeletedAt)
	// that are shared across most entity types in the system
	// These fields automatically track creation, update, and deletion timestamps
	Model // Embedded base model with ID and timestamp fields (created_at, updated_at, deleted_at)

	// UserName is the unique identifier for the user in the system.
	// It must not be empty and is indexed in the database.
	// This field is used for login purposes and must be unique across all users.
	// Validation ensures this field is never empty before persistence.
	// Users will use this value to identify themselves during authentication.
	// The uniqueness constraint prevents duplicate registrations and ensures system integrity.
	UserName string `json:"username" xml:"username" yaml:"username" toml:"username" schema:"username"  gorm:"column:username;not null;uniqueIndex:user_ids;default:'';"`
...

// Model represents the base structure that other domain models can embed.
// It provides standard fields for identification, creation time, update time,
// and soft deletion support through GORM's DeletedAt field.
type Model struct {
	// ID is the primary key for the model record in the database.
	ID id.ID `json:"id" xml:"id" yaml:"id" toml:"id" schema:"id" gorm:"primaryKey;autoIncrement;column:id"`
	// CreatedAt stores the timestamp when the record was initially created.
	CreatedAt time.Time `json:"created_at,omitempty" xml:"created_at,omitempty"  yaml:"created_at,omitempty" toml:"created_at,omitempty" schema:"created_at,omitempty" gorm:"column:created_at"`
	// UpdatedAt stores the timestamp when the record was last updated.
	UpdatedAt time.Time `json:"updated_at,omitempty" xml:"updated_at,omitempty" yaml:"updated_at,omitempty"  toml:"updated_at,omitempty" schema:"updated_at,omitempty" gorm:"column:updated_at"`
	// DeletedAt supports soft deletion (when set, the record is considered deleted).
	DeletedAt gorm.DeletedAt `json:"deleted_at,omitempty" xml:"deleted_at,omitempty"  yaml:"deleted_at,omitempty" toml:"deleted_at,omitempty" schema:"deleted_at,omitempty" gorm:"index;column:deleted_at"`
}

To Reproduce
when i try to Marshal with toml, CreatedAt, UpdatedAt are skipped.
CreatedAt, UpdatedAt should be output after id.

version = '0.1'
code = 200
message = 'OK'
timestamp = 1747452058
requestid = 'd0k016ljcs8dudumnd40'

[data]
page = 1
limit = 30
total = 1

[[data.list]]
id = 1
username = 'snowdream'

Expected behavior
A clear and concise description of what you expected to happen, if other than "should work".

Versions

• go-toml: github.com/pelletier/go-toml/v2 v2.2.4
• go: go version
  go version go1.23.6 darwin/amd64
• operating system: e.g. macOS

Additional context
Add any other context about the problem here that you think may help to diagnose.

[NathanBaulch]

I ran into this same issue today - omitempty doesn't work with time.Time values, which have no exported fields and are therefore (rightly or wrongly) always assumed to be empty. FWIW, the OOTB json encoder doesn't work either unless you use json:",omitzero" instead.