The condition node

A fork in the road with two exits, decided by a CEL expression over the frame.

{
  "id": "confident",
  "type": "condition",
  "condition": "vars.score > 0.7 && vars.topic != 'billing'",
  "then": "answer",
  "else": "escalate"
}

• The expression is evaluated against the current frame and taken as a boolean, so an empty string, 0 and an empty list send execution down else as surely as false does.
• then is required. else is not.
• The node writes nothing to the frame — it only chooses. To carry a computed value onwards, write it with a stage before the fork, or with expose.
• The condition_evaluated event records what was decided: {"result": true, "next": "answer"}.

In the editor the variables the expression reads become data ports of the card, so a condition is not a black box on the canvas:

When the road ends

If the condition is false and there is no else, there is nowhere to go and the run simply ends: no terminal was reached, so the session returns result = null and no artifacts.

That is occasionally what is wanted — "nothing more to do here" — but far more often it is a forgotten branch. When the end of a road is deliberate, say so with a terminal: the result then states which end it was.