Skip to content

Use Optional Variables

Mark variables as optional to handle cases where data may be missing or unset, allowing your flow to continue gracefully instead of failing.

QType YAML

variables:
  - id: email
    type: text?           # Optional text variable

Explanation

  • ? suffix: Shorthand syntax to mark a variable as optional
  • Optional variables: Can be None or set to a value
  • FieldExtractor: Returns None for optional output variables when JSONPath finds no matches, instead of raising an error. If you make the variable non-optional, it will raise an error.

Complete Example

id: optional_variables_demo
description: Demonstrates optional variables that can handle missing data gracefully

flows:
  - id: extract_optional_field
    variables:
      - id: user_profile
        type: text
      - id: email
        type: text?

    inputs:
      - user_profile
    outputs:
      - email

    steps:
      # Try to extract email - may not exist, will return None if missing
      - type: FieldExtractor
        id: extract_email
        inputs:
          - user_profile
        outputs:
          - email
        json_path: $.email

      - type: Echo
        id: show_result
        inputs:
          - email
        outputs:
          - email

Run it: 

# When email field exists
qtype run examples/language_features/optional_variables.qtype.yaml -i '{"user_profile": {"email":"hello@domain.com"}}'
# Results:                                                                                          
# email: hello@domain.com

# When email field is missing
qtype run examples/language_features/optional_variables.qtype.yaml -i '{"user_profile": "just text"}'
# Results:                                                                                          
# email: None

See Also