Transactional api sends empty subject when subject does not contain template string "{{"

[eddywashere]

Version:

• listmonk: 2.2.0
• OS: Ubuntu 20
• Mailgun smtp

Description of the bug and steps to reproduce:

The email subject is empty when sending transactional emails via /api/tx and the subject of the template does not contain a template string.

Screenshots:

Transactional Template without template string in subject

POST `/api/tx`

{
	"subscriber_email": "me@example.com",
	"template_id": 5
	"content_type": "html"
}

Transactional Template with template string in subject

POST `/api/tx`

{
	"subscriber_email": "me@example.com",
	"template_id": 5,
	"data": { "subject": "this is a custom subject2" },
	"content_type": "html"
}

[knadh]

Thanks for reporting. Will investigate this shortly.