[flow engine] Selectors don't support || and && operators — AI agents naturally write them

[lucasygu]

Summary

The flow engine's selector parser treats the entire expression as a single dot-path lookup. When AI agents write natural JavaScript patterns like $.input.maxResults || 10 (default fallback) or $.input.email && $.input.email.length > 0 (conditional check), the engine tries to find an input named maxResults || 10 — which doesn't exist — and fails validation.

Reproduction

The || pattern (default values)

{
  "id": "search",
  "type": "action",
  "action": {
    "data": {
      "numResults": "$.input.maxResults || 10"
    }
  }
}

Validation error: Selector "$.input.maxResults || 10" references undefined input "maxResults || 10"

The && pattern (conditional checks)

{
  "id": "sendEmail",
  "type": "action",
  "if": "$.input.recipientEmail && $.input.recipientEmail.length > 0",
  "action": { ... }
}

Validation error: Selector "$.input.recipientEmail && $.input.recipientEmail.length > 0" references undefined input "recipientEmail && $"

Why AI agents write this

Both patterns are idiomatic JavaScript. When an AI agent designs a workflow with optional inputs, $.input.x || defaultValue is the natural way to express "use this input if provided, otherwise fall back to a default." Similarly, $.input.x && $.input.x.length > 0 is the natural null-safe check before using an optional string.

How often this happens

We built 65 n8n-replicated flows in a single session. This issue appeared in:

• 2 flows with && in if conditions (go-to-marketing, research-agent)
• 2 flows with || default fallbacks (google-maps-scraper, scrape-leads-google-maps)

That's 4 out of 65 (6%) — frequent enough that any batch of AI-generated flows will hit it.

Current workarounds

For || defaults: Declare the default in the input definition and reference $.input.x directly:

{
  "inputs": {
    "maxResults": { "type": "number", "default": 10 }
  },
  "steps": [{
    "action": { "data": { "numResults": "$.input.maxResults" } }
  }]
}

For && conditionals: Simplify to a truthy check:

{
  "if": "$.input.recipientEmail"
}

Suggested fix

Either:

Option A: Expand the selector parser to support || and && as JavaScript expressions (evaluate them at runtime instead of treating the whole string as a dot-path).

Option B: Document the limitation in the skill's selector syntax reference and add a validation error message that suggests the workaround:

Selector "$.input.maxResults || 10" contains unsupported operator "||". 
Use the "default" field on the input definition instead, or use a "code" step for complex expressions.

Option B is lower effort and would prevent AI agents from hitting a confusing error.

Related

This is the same class of issue as:

• cli#6 (default values not resolved — now fixed in 1.14.1)
• cli#12 (parseJson:true fails — skill teaches a pattern that doesn't work)

All three are cases where the flow engine's behavior surprises AI agents that write natural JavaScript patterns.