diff --git a/internal/transformer/customer_transformer.go b/internal/transformer/customer_transformer.go
index 72812af..69b9618 100644
--- a/internal/transformer/customer_transformer.go
+++ b/internal/transformer/customer_transformer.go
@@ -45,6 +45,10 @@ func SetDefaultCustomerRequestToModel(req *contract.SetDefaultCustomerRequest) *
 
 // Model to Contract conversions
 func CustomerModelToResponse(customer *models.CustomerResponse) *contract.CustomerResponse {
+	if customer == nil {
+		return nil
+	}
+
 	return &contract.CustomerResponse{
 		ID:             customer.ID,
 		OrganizationID: customer.OrganizationID,
diff --git a/internal/transformer/gamification_transformer.go b/internal/transformer/gamification_transformer.go
index a178466..4b2d035 100644
--- a/internal/transformer/gamification_transformer.go
+++ b/internal/transformer/gamification_transformer.go
@@ -30,11 +30,20 @@ func ListCustomerPointsRequestToModel(req *contract.ListCustomerPointsRequest) *
 }
 
 func CustomerPointsModelToResponse(model *models.CustomerPointsResponse) *contract.CustomerPointsResponse {
+	if model == nil {
+		return nil
+	}
+
+	var customer *contract.CustomerResponse
+	if model.Customer != nil {
+		customer = CustomerModelToResponse(model.Customer)
+	}
+
 	return &contract.CustomerPointsResponse{
 		ID:         model.ID,
 		CustomerID: model.CustomerID,
 		Balance:    model.Balance,
-		Customer:   CustomerModelToResponse(model.Customer),
+		Customer:   customer,
 		CreatedAt:  model.CreatedAt,
 		UpdatedAt:  model.UpdatedAt,
 	}
@@ -82,12 +91,21 @@ func ListCustomerTokensRequestToModel(req *contract.ListCustomerTokensRequest) *
 }
 
 func CustomerTokensModelToResponse(model *models.CustomerTokensResponse) *contract.CustomerTokensResponse {
+	if model == nil {
+		return nil
+	}
+
+	var customer *contract.CustomerResponse
+	if model.Customer != nil {
+		customer = CustomerModelToResponse(model.Customer)
+	}
+
 	return &contract.CustomerTokensResponse{
 		ID:         model.ID,
 		CustomerID: model.CustomerID,
 		TokenType:  model.TokenType,
 		Balance:    model.Balance,
-		Customer:   CustomerModelToResponse(model.Customer),
+		Customer:   customer,
 		CreatedAt:  model.CreatedAt,
 		UpdatedAt:  model.UpdatedAt,
 	}
@@ -193,6 +211,10 @@ func ListGamesRequestToModel(req *contract.ListGamesRequest) *models.ListGamesQu
 }
 
 func GameModelToResponse(model *models.GameResponse) *contract.GameResponse {
+	if model == nil {
+		return nil
+	}
+
 	return &contract.GameResponse{
 		ID:        model.ID,
 		Name:      model.Name,
@@ -265,6 +287,20 @@ func ListGamePrizesRequestToModel(req *contract.ListGamePrizesRequest) *models.L
 }
 
 func GamePrizeModelToResponse(model *models.GamePrizeResponse) *contract.GamePrizeResponse {
+	if model == nil {
+		return nil
+	}
+
+	var game *contract.GameResponse
+	if model.Game != nil {
+		game = GameModelToResponse(model.Game)
+	}
+
+	var fallbackPrize *contract.GamePrizeResponse
+	if model.FallbackPrize != nil {
+		fallbackPrize = GamePrizeModelToResponse(model.FallbackPrize)
+	}
+
 	return &contract.GamePrizeResponse{
 		ID:              model.ID,
 		GameID:          model.GameID,
@@ -275,8 +311,8 @@ func GamePrizeModelToResponse(model *models.GamePrizeResponse) *contract.GamePri
 		Threshold:       model.Threshold,
 		FallbackPrizeID: model.FallbackPrizeID,
 		Metadata:        model.Metadata,
-		Game:            GameModelToResponse(model.Game),
-		FallbackPrize:   GamePrizeModelToResponse(model.FallbackPrize),
+		Game:            game,
+		FallbackPrize:   fallbackPrize,
 		CreatedAt:       model.CreatedAt,
 		UpdatedAt:       model.UpdatedAt,
 	}
@@ -337,6 +373,25 @@ func ListGamePlaysRequestToModel(req *contract.ListGamePlaysRequest) *models.Lis
 }
 
 func GamePlayModelToResponse(model *models.GamePlayResponse) *contract.GamePlayResponse {
+	if model == nil {
+		return nil
+	}
+
+	var game *contract.GameResponse
+	if model.Game != nil {
+		game = GameModelToResponse(model.Game)
+	}
+
+	var customer *contract.CustomerResponse
+	if model.Customer != nil {
+		customer = CustomerModelToResponse(model.Customer)
+	}
+
+	var prize *contract.GamePrizeResponse
+	if model.Prize != nil {
+		prize = GamePrizeModelToResponse(model.Prize)
+	}
+
 	return &contract.GamePlayResponse{
 		ID:         model.ID,
 		GameID:     model.GameID,
@@ -345,16 +400,35 @@ func GamePlayModelToResponse(model *models.GamePlayResponse) *contract.GamePlayR
 		TokenUsed:  model.TokenUsed,
 		RandomSeed: model.RandomSeed,
 		CreatedAt:  model.CreatedAt,
-		Game:       GameModelToResponse(model.Game),
-		Customer:   CustomerModelToResponse(model.Customer),
-		Prize:      GamePrizeModelToResponse(model.Prize),
+		Game:       game,
+		Customer:   customer,
+		Prize:      prize,
 	}
 }
 
 func PlayGameModelToResponse(model *models.PlayGameResponse) *contract.PlayGameResponse {
+	if model == nil {
+		return nil
+	}
+
+	var gamePlay *contract.GamePlayResponse
+	if &model.GamePlay != nil {
+		gamePlay = GamePlayModelToResponse(&model.GamePlay)
+	}
+
+	var prizeWon *contract.GamePrizeResponse
+	if model.PrizeWon != nil {
+		prizeWon = GamePrizeModelToResponse(model.PrizeWon)
+	}
+
+	var gamePlayValue contract.GamePlayResponse
+	if gamePlay != nil {
+		gamePlayValue = *gamePlay
+	}
+
 	return &contract.PlayGameResponse{
-		GamePlay:        *GamePlayModelToResponse(&model.GamePlay),
-		PrizeWon:        GamePrizeModelToResponse(model.PrizeWon),
+		GamePlay:        gamePlayValue,
+		PrizeWon:        prizeWon,
 		TokensRemaining: model.TokensRemaining,
 	}
 }
@@ -410,6 +484,15 @@ func ListOmsetTrackerRequestToModel(req *contract.ListOmsetTrackerRequest) *mode
 }
 
 func OmsetTrackerModelToResponse(model *models.OmsetTrackerResponse) *contract.OmsetTrackerResponse {
+	if model == nil {
+		return nil
+	}
+
+	var game *contract.GameResponse
+	if model.Game != nil {
+		game = GameModelToResponse(model.Game)
+	}
+
 	return &contract.OmsetTrackerResponse{
 		ID:          model.ID,
 		PeriodType:  model.PeriodType,
@@ -417,7 +500,7 @@ func OmsetTrackerModelToResponse(model *models.OmsetTrackerResponse) *contract.O
 		PeriodEnd:   model.PeriodEnd,
 		Total:       model.Total,
 		GameID:      model.GameID,
-		Game:        GameModelToResponse(model.Game),
+		Game:        game,
 		CreatedAt:   model.CreatedAt,
 		UpdatedAt:   model.UpdatedAt,
 	}
diff --git a/migrations/000057_add_customer_password_field.up.sql b/migrations/000057_add_customer_password_field.up.sql
new file mode 100644
index 0000000..af613c2
--- /dev/null
+++ b/migrations/000057_add_customer_password_field.up.sql
@@ -0,0 +1,17 @@
+-- Add password field to customers table for authentication
+ALTER TABLE customers ADD COLUMN password_hash VARCHAR(255);
+
+-- Add phone number field if not exists (for registration)
+ALTER TABLE customers ADD COLUMN phone_number VARCHAR(20) UNIQUE;
+
+-- Add birth_date field for customer registration
+ALTER TABLE customers ADD COLUMN birth_date DATE;
+
+-- Add indexes for better performance
+CREATE INDEX idx_customers_phone_number ON customers(phone_number);
+CREATE INDEX idx_customers_password_hash ON customers(password_hash) WHERE password_hash IS NOT NULL;
+
+-- Add comments
+COMMENT ON COLUMN customers.password_hash IS 'Hashed password for customer authentication';
+COMMENT ON COLUMN customers.phone_number IS 'Unique phone number for customer login';
+COMMENT ON COLUMN customers.birth_date IS 'Customer birth date for registration';