Workflow API ignores default values for optional input variables

[importcjj]

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Dify version

1.10.0

Cloud or Self Hosted

Self Hosted (Docker)

Steps to reproduce

1. Create a workflow with a start node
2. Add an optional input variable with a default value (e.g., text input with default "hello")
3. Call the workflow API without providing that optional field
4. The variable receives null instead of the default value "hello"

✔️ Expected Behavior

Optional workflow input variables should use their configured default values when not provided in the API request.

❌ Actual Behavior

Optional variables receive null when omitted from the API request, ignoring the default value configuration.

[dosubot]

This is a confirmed limitation in Dify v1.10.0: when you call the workflow API and omit optional input variables that have default values configured, those variables are set to null instead of using their defaults. The backend does not currently apply default values for omitted optional inputs—defaults are only respected in the UI, not in API-driven workflows. This behavior is due to how the API controller and input preparation logic work: if an input is missing, it stays as None/null and the default is ignored in the backend flow (source).

Until this is fixed, the best workaround is to always provide all input variables in your API payload, even if they have defaults set in the workflow editor (source). There is no backend config or flag to change this behavior at the moment. If you want to track or contribute to a fix, the relevant logic is in the input preparation and workflow start node code (source, source).

To reply, just mention @dosu.

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