diff --git a/repositories/alias.go b/repositories/alias.go
index 676d0df..7c1f05a 100644
--- a/repositories/alias.go
+++ b/repositories/alias.go
@@ -24,6 +24,9 @@ func (r *AliasRepository) GetAll() ([]*models.Alias, error) {
 
 func (r *AliasRepository) GetByUser(userId string) ([]*models.Alias, error) {
 	var aliases []*models.Alias
+	if userId == "" {
+		return aliases, nil
+	}
 	if err := r.db.
 		Where(&models.Alias{UserID: userId}).
 		Find(&aliases).Error; err != nil {
@@ -34,6 +37,9 @@ func (r *AliasRepository) GetByUser(userId string) ([]*models.Alias, error) {
 
 func (r *AliasRepository) GetByUserAndKey(userId, key string) ([]*models.Alias, error) {
 	var aliases []*models.Alias
+	if userId == "" {
+		return aliases, nil
+	}
 	if err := r.db.
 		Where(&models.Alias{
 			UserID: userId,
@@ -47,6 +53,9 @@ func (r *AliasRepository) GetByUserAndKey(userId, key string) ([]*models.Alias,
 
 func (r *AliasRepository) GetByUserAndKeyAndType(userId, key string, summaryType uint8) ([]*models.Alias, error) {
 	var aliases []*models.Alias
+	if userId == "" {
+		return aliases, nil
+	}
 	if err := r.db.
 		Where(&models.Alias{
 			UserID: userId,
@@ -61,6 +70,9 @@ func (r *AliasRepository) GetByUserAndKeyAndType(userId, key string, summaryType
 
 func (r *AliasRepository) GetByUserAndTypeAndValue(userId string, summaryType uint8, value string) (*models.Alias, error) {
 	alias := &models.Alias{}
+	if userId == "" {
+		return nil, errors.New("invalid input")
+	}
 	if err := r.db.
 		Where(&models.Alias{
 			UserID: userId,
diff --git a/repositories/language_mapping.go b/repositories/language_mapping.go
index 1d0c029..f6fcf14 100644
--- a/repositories/language_mapping.go
+++ b/repositories/language_mapping.go
@@ -34,6 +34,9 @@ func (r *LanguageMappingRepository) GetById(id uint) (*models.LanguageMapping, e
 
 func (r *LanguageMappingRepository) GetByUser(userId string) ([]*models.LanguageMapping, error) {
 	var mappings []*models.LanguageMapping
+	if userId == "" {
+		return mappings, nil
+	}
 	if err := r.db.
 		Where(&models.LanguageMapping{UserID: userId}).
 		Find(&mappings).Error; err != nil {
diff --git a/repositories/project_label.go b/repositories/project_label.go
index 7c87ef0..05320b3 100644
--- a/repositories/project_label.go
+++ b/repositories/project_label.go
@@ -33,6 +33,9 @@ func (r *ProjectLabelRepository) GetById(id uint) (*models.ProjectLabel, error)
 }
 
 func (r *ProjectLabelRepository) GetByUser(userId string) ([]*models.ProjectLabel, error) {
+	if userId == "" {
+		return []*models.ProjectLabel{}, nil
+	}
 	var labels []*models.ProjectLabel
 	if err := r.db.
 		Where(&models.ProjectLabel{UserID: userId}).
diff --git a/repositories/user.go b/repositories/user.go
index 69e4e29..abc833c 100644
--- a/repositories/user.go
+++ b/repositories/user.go
@@ -35,6 +35,9 @@ func (r *UserRepository) GetByIds(userIds []string) ([]*models.User, error) {
 }
 
 func (r *UserRepository) GetByApiKey(key string) (*models.User, error) {
+	if key == "" {
+		return nil, errors.New("invalid input")
+	}
 	u := &models.User{}
 	if err := r.db.Where(&models.User{ApiKey: key}).First(u).Error; err != nil {
 		return u, err