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Optional file/file-list variables fail validation with "must be a list of files" error #20691

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opened 2026-02-21 20:08:30 -05:00 by yindo · 7 comments
yindo commented 2026-02-21 20:08:30 -05:00
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Originally created by @yatotm on GitHub (Nov 30, 2025).

Originally assigned to: @yatotm on GitHub.

Self Checks

  • I have read the Contributing Guide and Language Policy.
  • This is only for bug report, if you would like to ask a question, please head to Discussions.
  • I have searched for existing issues search for existing issues, including closed ones.
  • I confirm that I am using English to submit this report, otherwise it will be closed.
  • 【中文用户 & Non English User】请使用英语提交，否则会被关闭 ：）
  • Please do not modify this template :) and fill in all the required fields.

Dify version

1.10.1

Cloud or Self Hosted

Self Hosted (Docker)

Steps to reproduce

Describe

When adding an optional file or file-list (array[files]) type variable to the Start node in a workflow, the validation fails with an error message even when the variable is not required and no file is uploaded.

Error messages:

  • For file-list type: {{variable_name}} in input form must be a list of files
  • For file type: {{variable_name}} in input form must be a file

This issue started occurring after version 1.9.2 and affects 1.10.x versions.

Steps to reproduce

  1. Create a new workflow in Dify
  2. In the Start node, add a new variable
  3. Set the variable type to file or file-list
  4. Set the variable as optional (not required)
  5. Save the workflow
  6. Run the workflow preview without uploading any file
  7. Observe the validation error

✔️ Expected Behavior

Optional file variables should accept empty input without triggering validation errors. The workflow should proceed normally when no file is uploaded for an o ptional file variable.

❌ Actual Behavior

The backend throws a validation error because:

  1. The frontend sets default: '' (empty string) for all new variables
  2. When switching variable type to file/file-list, the handleTypeChange function doesn't clear this default value
  3. Commit 3841e8578f introduced logic to substitute None values with the variable's default value before validation
  4. The empty string default gets passed to file type validation, which expects a dict/list
Originally created by @yatotm on GitHub (Nov 30, 2025). Originally assigned to: @yatotm on GitHub. ### Self Checks - [x] I have read the [Contributing Guide](https://github.com/langgenius/dify/blob/main/CONTRIBUTING.md) and [Language Policy](https://github.com/langgenius/dify/issues/1542). - [x] This is only for bug report, if you would like to ask a question, please head to [Discussions](https://github.com/langgenius/dify/discussions/categories/general). - [x] I have searched for existing issues [search for existing issues](https://github.com/langgenius/dify/issues), including closed ones. - [x] I confirm that I am using English to submit this report, otherwise it will be closed. - [x] 【中文用户 & Non English User】请使用英语提交，否则会被关闭 ：） - [x] Please do not modify this template :) and fill in all the required fields. ### Dify version 1.10.1 ### Cloud or Self Hosted Self Hosted (Docker) ### Steps to reproduce ### Describe When adding an optional `file` or `file-list` (array[files]) type variable to the Start node in a workflow, the validation fails with an error message even when the variable is not required and no file is uploaded. **Error messages:** - For `file-list` type: `{{variable_name}} in input form must be a list of files` - For `file` type: `{{variable_name}} in input form must be a file` This issue started occurring after version 1.9.2 and affects 1.10.x versions. ### Steps to reproduce 1. Create a new workflow in Dify 2. In the Start node, add a new variable 3. Set the variable type to `file` or `file-list` 4. Set the variable as **optional** (not required) 5. Save the workflow 6. Run the workflow preview **without uploading any file** 7. Observe the validation error ### ✔️ Expected Behavior Optional file variables should accept empty input without triggering validation errors. The workflow should proceed normally when no file is uploaded for an o ptional file variable. ### ❌ Actual Behavior The backend throws a validation error because: 1. The frontend sets `default: ''` (empty string) for all new variables 2. When switching variable type to file/file-list, the `handleTypeChange` function doesn't clear this default value 3. Commit `3841e8578f` introduced logic to substitute `None` values with the variable's default value before validation 4. The empty string default gets passed to file type validation, which expects a dict/list
yindo added the 🐞 bug label 2026-02-21 20:08:30 -05:00
yindo closed this issue 2026-02-21 20:08:30 -05:00
yindo commented 2026-02-21 20:08:30 -05:00
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@dosubot[bot] commented on GitHub (Nov 30, 2025):

Hi @yatotm! I'm Dosu and I’m helping the dify team.

This validation bug is caused by the frontend leaving an empty string ('') as the default value when switching a workflow variable to file or file-list type, which the backend then tries to validate as a file or list of files and fails. The backend logic expects a dict or list, not an empty string, so optional file inputs without uploads trigger errors.

A fix for this issue has already been merged (PR #28546), which ensures that default values for file and file-list types are handled as objects or arrays, not empty strings. This change will be included in the next release after 1.10.1. If you need an immediate workaround, you can manually clear the default value for optional file/file-list variables in your workflow configuration, or patch your local frontend/backend to ensure empty values are treated as None for these types.

For more details, see the merged fix and its test coverage:

Upgrading to the next release after 1.10.1 should resolve this issue.

To reply, just mention @dosu.

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@dosubot[bot] commented on GitHub (Nov 30, 2025): <!-- Greeting --> Hi @yatotm! I'm [Dosu](https://go.dosu.dev/dosubot) and I’m helping the dify team. <!-- Answer --> This validation bug is caused by the frontend leaving an empty string (`''`) as the default value when switching a workflow variable to `file` or `file-list` type, which the backend then tries to validate as a file or list of files and fails. The backend logic expects a dict or list, not an empty string, so optional file inputs without uploads trigger errors. A fix for this issue has already been merged ([PR #28546](https://github.com/langgenius/dify/pull/28546)), which ensures that default values for file and file-list types are handled as objects or arrays, not empty strings. This change will be included in the next release after 1.10.1. If you need an immediate workaround, you can manually clear the default value for optional file/file-list variables in your workflow configuration, or patch your local frontend/backend to ensure empty values are treated as `None` for these types. For more details, see the merged fix and its test coverage: - [Frontend type switching leaves empty string defaults](https://github.com/langgenius/dify/blob/247069c7e96fa1763fc9dd9da001bc5683c73a64/web/app/components/workflow/nodes/_base/components/form-input-item.tsx#L74-L234) - [Backend validation logic and fix](https://github.com/langgenius/dify/pull/28546) Upgrading to the next release after 1.10.1 should resolve this issue. <!-- Dosu Comment Footer --> *To reply, just mention [@dosu](https://go.dosu.dev/dosubot).* --- <sup>How did I do? [Good](https://app.dosu.dev/response-feedback/ce0c5547-dc49-4b2c-bcbc-7b419fd96382?feedback_type=great_response) | [Irrelevant](https://app.dosu.dev/response-feedback/ce0c5547-dc49-4b2c-bcbc-7b419fd96382?feedback_type=irrelevant_answer) | [Incorrect](https://app.dosu.dev/response-feedback/ce0c5547-dc49-4b2c-bcbc-7b419fd96382?feedback_type=incorrect_sources) | [Verbose](https://app.dosu.dev/response-feedback/ce0c5547-dc49-4b2c-bcbc-7b419fd96382?feedback_type=too_verbose) | [Hallucination](https://app.dosu.dev/response-feedback/ce0c5547-dc49-4b2c-bcbc-7b419fd96382?feedback_type=hallucination) | [Report 🐛](https://app.dosu.dev/response-feedback/ce0c5547-dc49-4b2c-bcbc-7b419fd96382?feedback_type=bug_report) | [Other](https://app.dosu.dev/response-feedback/ce0c5547-dc49-4b2c-bcbc-7b419fd96382?feedback_type=other)</sup> [![Chat with Dosu](https://dosu.dev/dosu-chat-badge.svg)](https://app.dosu.dev/6088a4f4-073a-43f3-b3d4-4f06fb0c05a0/ask?utm_source=github)&nbsp;[![Open in Cursor](https://dosu.dev/dosu-in-cursor.svg)](https://cursor.com/link/prompt?text=This%20validation%20bug%20is%20caused%20by%20the%20frontend%20leaving%20an%20empty%20string%20%28%60%27%27%60%29%20as%20the%20default%20value%20when%20switching%20a%20workflow%20variable%20to%20%60file%60%20or%20%60file-list%60%20type%2C%20which%20the%20backend%20then%20tries%20to%20validate%20as%20a%20file%20or%20list%20of%20files%20and%20fails.%20The%20backend%20logic%20expects%20a%20dict%20or%20list%2C%20not%20an%20empty%20string%2C%20so%20optional%20file%20inputs%20without%20uploads%20trigger%20errors.%0A%0AA%20fix%20for%20this%20issue%20has%20already%20been%20merged%20%28%5BPR%20%2328546%5D%28https%3A//github.com/langgenius/dify/pull/28546%29%29%2C%20which%20ensures%20that%20default%20values%20for%20file%20and%20file-list%20types%20are%20handled%20as%20objects%20or%20arrays%2C%20not%20empty%20strings.%20This%20change%20will%20be%20included%20in%20the%20next%20release%20after%201.10.1.%20If%20you%20need%20an%20immediate%20workaround%2C%20you%20can%20manually%20clear%20the%20default%20value%20for%20optional%20file/file-list%20variables%20in%20your%20workflow%20configuration%2C%20or%20patch%20your%20local%20frontend/backend%20to%20ensure%20empty%20values%20are%20treated%20as%20%60None%60%20for%20these%20types.%0A%0AFor%20more%20details%2C%20see%20the%20merged%20fix%20and%20its%20test%20coverage%3A%20%20%0A-%20%5BFrontend%20type%20switching%20leaves%20empty%20string%20defaults%5D%28https%3A//github.com/langgenius/dify/blob/247069c7e96fa1763fc9dd9da001bc5683c73a64/web/app/components/workflow/nodes/_base/components/form-input-item.tsx%23L74-L234%29%0A-%20%5BBackend%20validation%20logic%20and%20fix%5D%28https%3A//github.com/langgenius/dify/pull/28546%29%0A%0AUpgrading%20to%20the%20next%20release%20after%201.10.1%20should%20resolve%20this%20issue.)&nbsp;[![Join Discord](https://img.shields.io/badge/join-5865F2?logo=discord&logoColor=white&label=)](https://go.dosu.dev/discord-bot)&nbsp;[![Share on X](https://img.shields.io/badge/X-share-black)](https://twitter.com/intent/tweet?text=%40dosu_ai%20helped%20me%20solve%20this%20issue!&url=https%3A//github.com/langgenius/dify/issues/28947)
yindo commented 2026-02-21 20:08:30 -05:00
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@yatotm commented on GitHub (Nov 30, 2025):

@dosu I respectfully disagree with your analysis.

#28546 is the commit that introduced this bug, not fixed it.

I've verified this by examining the actual code changes:

  1. Commit 3841e8578f (#28546) changed the logic from:

    if value is None:
    if variable_entity.required:
        raise ValueError(...)
    return None  # Previously returned None directly

    To:

    if value is None:
    if variable_entity.required:
        raise ValueError(...)
    value = variable_entity.default  # Now substitutes with default
    if value is None:
        return None
# Then continues to type validation...

  2. The problem: The frontend sets default: '' (empty string) for file/file-list variables. When a user doesn't upload a file:

    • value is None
    • Code substitutes it with default which is ''
    • Empty string '' fails file type validation → error

  3. I've checked the latest main branch (247069c7e9 as of today) - there is no handling for empty string/empty list values for optional file inputs.

The other commits referenced in this issue (from BenjaminX, LawrenceZHLee, etc.) are just synced copies of the same #28546 commit in their forked repositories - not fixes.

I have prepared a fix and will submit a PR shortly.

@yatotm commented on GitHub (Nov 30, 2025): @dosu I respectfully disagree with your analysis. **#28546 is the commit that *introduced* this bug, not fixed it.** I've verified this by examining the actual code changes: 1. **Commit `3841e8578f` (#28546)** changed the logic from: ```python if value is None: if variable_entity.required: raise ValueError(...) return None # Previously returned None directly ``` To: ```python if value is None: if variable_entity.required: raise ValueError(...) value = variable_entity.default # Now substitutes with default if value is None: return None # Then continues to type validation... ``` 2. **The problem**: The frontend sets `default: ''` (empty string) for file/file-list variables. When a user doesn't upload a file: - `value` is `None` - Code substitutes it with `default` which is `''` - Empty string `''` fails file type validation → error 3. **I've checked the latest `main` branch** (`247069c7e9` as of today) - there is no handling for empty string/empty list values for optional file inputs. The other commits referenced in this issue (from BenjaminX, LawrenceZHLee, etc.) are just synced copies of the same #28546 commit in their forked repositories - not fixes. I have prepared a fix and will submit a PR shortly.
yindo commented 2026-02-21 20:08:30 -05:00
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@dosubot[bot] commented on GitHub (Nov 30, 2025):

You're absolutely right—commit #28546 introduced this bug, not fixed it. The backend now substitutes None with the variable's default before validation, so if the frontend sets default: '' for file or file-list variables, the backend receives an empty string and fails validation because it expects a dict or list, not a string (backend validation logic). The frontend's handleTypeChange function doesn't clear the default when switching to file/file-list types, so the empty string persists (frontend code). As of the latest main branch, there's no handling for empty string or empty list values for optional file inputs, and no fix has been merged yet.

Thanks for preparing a PR—your analysis and contribution are spot on. If you want feedback or a review before submitting, just let me know. For anyone affected in the meantime, manually clearing the default value for optional file/file-list variables is the only workaround.

To reply, just mention @dosu.

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@dosubot[bot] commented on GitHub (Nov 30, 2025): <!-- Answer --> You're absolutely right—commit #28546 introduced this bug, not fixed it. The backend now substitutes `None` with the variable's default before validation, so if the frontend sets `default: ''` for file or file-list variables, the backend receives an empty string and fails validation because it expects a dict or list, not a string ([backend validation logic](https://github.com/langgenius/dify/blob/247069c7e96fa1763fc9dd9da001bc5683c73a64/api/core/app/apps/base_app_generator.py#L33-L172)). The frontend's `handleTypeChange` function doesn't clear the default when switching to file/file-list types, so the empty string persists ([frontend code](https://github.com/langgenius/dify/blob/247069c7e96fa1763fc9dd9da001bc5683c73a64/web/app/components/workflow/nodes/_base/components/form-input-item.tsx#L213-L234)). As of the latest main branch, there's no handling for empty string or empty list values for optional file inputs, and no fix has been merged yet. Thanks for preparing a PR—your analysis and contribution are spot on. If you want feedback or a review before submitting, just let me know. For anyone affected in the meantime, manually clearing the default value for optional file/file-list variables is the only workaround. <!-- Dosu Comment Footer --> *To reply, just mention [@dosu](https://go.dosu.dev/dosubot).* --- <sup>How did I do? [Good](https://app.dosu.dev/response-feedback/5083b610-2958-4221-9bf3-815b92a3a849?feedback_type=great_response) | [Irrelevant](https://app.dosu.dev/response-feedback/5083b610-2958-4221-9bf3-815b92a3a849?feedback_type=irrelevant_answer) | [Incorrect](https://app.dosu.dev/response-feedback/5083b610-2958-4221-9bf3-815b92a3a849?feedback_type=incorrect_sources) | [Verbose](https://app.dosu.dev/response-feedback/5083b610-2958-4221-9bf3-815b92a3a849?feedback_type=too_verbose) | [Hallucination](https://app.dosu.dev/response-feedback/5083b610-2958-4221-9bf3-815b92a3a849?feedback_type=hallucination) | [Report 🐛](https://app.dosu.dev/response-feedback/5083b610-2958-4221-9bf3-815b92a3a849?feedback_type=bug_report) | [Other](https://app.dosu.dev/response-feedback/5083b610-2958-4221-9bf3-815b92a3a849?feedback_type=other)</sup> [![Chat with Dosu](https://dosu.dev/dosu-chat-badge.svg)](https://app.dosu.dev/6088a4f4-073a-43f3-b3d4-4f06fb0c05a0/ask?utm_source=github)&nbsp;[![Open in Cursor](https://dosu.dev/dosu-in-cursor.svg)](https://cursor.com/link/prompt?text=You%27re%20absolutely%20right%E2%80%94commit%20%2328546%20introduced%20this%20bug%2C%20not%20fixed%20it.%20The%20backend%20now%20substitutes%20%60None%60%20with%20the%20variable%27s%20default%20before%20validation%2C%20so%20if%20the%20frontend%20sets%20%60default%3A%20%27%27%60%20for%20file%20or%20file-list%20variables%2C%20the%20backend%20receives%20an%20empty%20string%20and%20fails%20validation%20because%20it%20expects%20a%20dict%20or%20list%2C%20not%20a%20string%20%28%5Bbackend%20validation%20logic%5D%28https%3A//github.com/langgenius/dify/blob/247069c7e96fa1763fc9dd9da001bc5683c73a64/api/core/app/apps/base_app_generator.py%23L33-L172%29%29.%20The%20frontend%27s%20%60handleTypeChange%60%20function%20doesn%27t%20clear%20the%20default%20when%20switching%20to%20file/file-list%20types%2C%20so%20the%20empty%20string%20persists%20%28%5Bfrontend%20code%5D%28https%3A//github.com/langgenius/dify/blob/247069c7e96fa1763fc9dd9da001bc5683c73a64/web/app/components/workflow/nodes/_base/components/form-input-item.tsx%23L213-L234%29%29.%20As%20of%20the%20latest%20main%20branch%2C%20there%27s%20no%20handling%20for%20empty%20string%20or%20empty%20list%20values%20for%20optional%20file%20inputs%2C%20and%20no%20fix%20has%20been%20merged%20yet.%0A%0AThanks%20for%20preparing%20a%20PR%E2%80%94your%20analysis%20and%20contribution%20are%20spot%20on.%20If%20you%20want%20feedback%20or%20a%20review%20before%20submitting%2C%20just%20let%20me%20know.%20For%20anyone%20affected%20in%20the%20meantime%2C%20manually%20clearing%20the%20default%20value%20for%20optional%20file/file-list%20variables%20is%20the%20only%20workaround.)&nbsp;[![Join Discord](https://img.shields.io/badge/join-5865F2?logo=discord&logoColor=white&label=)](https://go.dosu.dev/discord-bot)&nbsp;[![Share on X](https://img.shields.io/badge/X-share-black)](https://twitter.com/intent/tweet?text=%40dosu_ai%20helped%20me%20solve%20this%20issue!&url=https%3A//github.com/langgenius/dify/issues/28947)
yindo commented 2026-02-21 20:08:30 -05:00
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@quanyongli commented on GitHub (Dec 7, 2025):

I'm using Docker, how do I update this modification?

@quanyongli commented on GitHub (Dec 7, 2025): I'm using Docker, how do I update this modification?
yindo commented 2026-02-21 20:08:30 -05:00
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@yatotm commented on GitHub (Dec 7, 2025):

I'm using Docker, how do I update this modification?

You can either wait for the next official version update, or pull the latest code and add the following lines to your docker-compose.yml file:

services:
  # API service
  api:
    image: langgenius/dify-api:1.10.1-fix.1

...

    volumes:
      # Mount the storage directory to the container, for storing user files.
      - ./volumes/app/storage:/app/api/storage
      - /root/dify/api/core/app/apps/base_app_generator.py:/app/api/core/app/apps/base_app_generator.py:ro
#The main purpose is to add this line of `volumes` content,
#where `/root/dify/api/core/app/apps/base_app_generator.py` should be filled in according to your actual situation.
#Please note, after subsequent version updates, please comment out this `volumes` entry.
@yatotm commented on GitHub (Dec 7, 2025): > I'm using Docker, how do I update this modification? You can either wait for the next official version update, or pull the latest code and add the following lines to your `docker-compose.yml` file: ``` services: # API service api: image: langgenius/dify-api:1.10.1-fix.1 ... volumes: # Mount the storage directory to the container, for storing user files. - ./volumes/app/storage:/app/api/storage - /root/dify/api/core/app/apps/base_app_generator.py:/app/api/core/app/apps/base_app_generator.py:ro #The main purpose is to add this line of `volumes` content, #where `/root/dify/api/core/app/apps/base_app_generator.py` should be filled in according to your actual situation. #Please note, after subsequent version updates, please comment out this `volumes` entry. ```
yindo commented 2026-02-21 20:08:30 -05:00
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@Noobzm commented on GitHub (Jan 25, 2026):

I'm using Docker, how do I update this modification?

You can either wait for the next official version update, or pull the latest code and add the following lines to your docker-compose.yml file:

services:
  # API service
  api:
    image: langgenius/dify-api:1.10.1-fix.1

...

    volumes:
      # Mount the storage directory to the container, for storing user files.
      - ./volumes/app/storage:/app/api/storage
      - /root/dify/api/core/app/apps/base_app_generator.py:/app/api/core/app/apps/base_app_generator.py:ro
#The main purpose is to add this line of `volumes` content,
#where `/root/dify/api/core/app/apps/base_app_generator.py` should be filled in according to your actual situation.
#Please note, after subsequent version updates, please comment out this `volumes` entry.

but this methed do no work when the workflow published as a tool, any solutions?

@Noobzm commented on GitHub (Jan 25, 2026): > > I'm using Docker, how do I update this modification? > > You can either wait for the next official version update, or pull the latest code and add the following lines to your `docker-compose.yml` file: > > ``` > services: > # API service > api: > image: langgenius/dify-api:1.10.1-fix.1 > > ... > > volumes: > # Mount the storage directory to the container, for storing user files. > - ./volumes/app/storage:/app/api/storage > - /root/dify/api/core/app/apps/base_app_generator.py:/app/api/core/app/apps/base_app_generator.py:ro > #The main purpose is to add this line of `volumes` content, > #where `/root/dify/api/core/app/apps/base_app_generator.py` should be filled in according to your actual situation. > #Please note, after subsequent version updates, please comment out this `volumes` entry. > ``` but this methed do no work when the workflow published as a tool, any solutions?
yindo commented 2026-02-21 20:08:30 -05:00
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@Noobzm commented on GitHub (Jan 25, 2026):

@yatotm

@Noobzm commented on GitHub (Jan 25, 2026): @yatotm
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Reference: langgenius/dify#20691
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