SMTP outbound connector - html and body content is null

[itsnuyen]

Describe the Bug

Because FEEL will take a string and a data and try to sum it, it will produce a null value.
This null value will produce a nullpointer as an error but the process is still running and after the defined retries it will break.
If you have multiple process running, this behavior will block everything else

Steps to Reproduce

1. Create a bpmn with a the outbound mail connector and use the SMTP feature
2. inside the mail content use following feel description
   "<h2>Test Test</h2>" + "hallo welt" + today()
3. deploy the BPMN and start a new process

Expected Behavior

When having a faulty body content, the connector should fail instantly and create a incident.

Environment

• OS: OSX Sequoia 15.2 as-well as kubernetes environment
• Camunda version: 8.6.5 (self-managed)