fix: use default values for optional workflow input variables (#28546)

[importcjj]

When calling workflow API with missing optional fields, they should use configured default values instead of becoming null.

Changes:

• Add default field to VariableEntity model
• Update _validate_inputs to pass default values through validation pipeline
• Ensure string number defaults (e.g., "123") are converted to proper types
• Add comprehensive test coverage for all supported variable types:
  • TEXT_INPUT, PARAGRAPH, SELECT - string defaults
  • NUMBER - int/float/string-formatted number defaults with type conversion
  • CHECKBOX - boolean defaults
  • FILE, FILE_LIST - object/array defaults

Fixes #28546

🤖 Generated with Claude Code

Important

1. Make sure you have read our contribution guidelines
2. Ensure there is an associated issue and you have been assigned to it
3. Use the correct syntax to link this PR: Fixes #<issue number>.

Summary

close [#28546 ]

Screenshots

Before	After
...	...

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[gemini-code-assist]

Summary of Changes

Hello @importcjj, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue where optional workflow input variables, when not explicitly provided, would default to null instead of utilizing their pre-configured default values. By introducing a default field in the VariableEntity and updating the input validation logic, the system now correctly applies these defaults, enhancing the reliability and predictability of workflow execution.

Highlights

• Model Enhancement: Introduced a default field of type Any to the VariableEntity model, allowing the definition of default values for workflow input variables.
• Input Validation Logic: Modified the _validate_inputs function to automatically use the configured default value from VariableEntity when an optional input variable is provided as None.
• Comprehensive Testing: Added extensive unit tests to test_base_app_generator.py to cover various scenarios for default values, including string, number, and explicit None defaults, and to ensure actual input values correctly override defaults.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request correctly implements the use of default values for optional workflow input variables. A default field has been added to VariableEntity, and the validation logic in _validate_inputs has been updated to use this default value when an optional input is missing. The changes are accompanied by comprehensive tests. My feedback focuses on improving the structure and maintainability of the new tests.

[crazywoola]

• Thanks for the PR :)
• Please link an existing issue or create a new issue and link it in the description.
• Please add some tests for the changes as well.