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How to set optional `Image or document input` to prompt?

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Posted on by SC-02030600-0

When using Prompt with `Image or document input` in Power Automate, that input parameter will become required, but I want it to be nullable.

I have tried passing null, an empty string, and "AA==" in the expression, but they will throw `Invalid input: Input parameters are invalid for your model` (`Unable to identify the mimetype input`).

Although the Text input of the prompt is marked as required in Power Automate, I can pass `null` to it without error. I just want to do the same thing to `Image or document input`.

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CedrickB Microsoft Employee on at

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Prompts multi modal inputs don't support null values.
There are 2 possible workarounds for you scenario:
1. Create a empty word file and export to PDF. When you want to pass a null document, send the empty PDF.
2. Create a copy of you prompt with same instruction but without document input. Call the original or the copy accordingly.

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Valantis 3,240 on at

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Hi @SC-02030600-0,

You can’t make “Image or document input” nullable in a prompt.

That input expects an actual file of a supported type sending null/empty triggers the MIME-type error you’re seeing.

There’s no documented setting to mark that input optional in Prompt builder.

try this workaround:

Build two prompts:

Prompt A: Text-only.

Prompt B: Text + Image or document input.

In your cloud flow, add a Condition before calling the prompt:

If your “File content” (or file reference) is empty, call Prompt A.

Else, call Prompt B and pass the file.

Example expressions you can use in the Condition:

empty(variables('FileContent'))

Or if you store the file in a property: empty(triggerBody()?['FileContent'])

Verify:

Run the flow twice—once with no file (should invoke Prompt A successfully) and once with a valid PNG/JPG/JPEG/PDF under the documented limits (should invoke Prompt B successfully).

Why this is necessary:

Image/document inputs require a real file and supported types and sizes; the docs list formats and limits but don’t provide an option to make the parameter optional. Passing null/empty means the runtime can’t determine a MIME type, which leads to the error. Source links below show the supported input types and prompt creation flow.

check also this links for more info:

Add inputs to your prompt (Image or document input, supported types and limits): https://learn.microsoft.com/microsoft-copilot-studio/add-inputs-prompt#image-or-document-input

Add inputs to your prompt (Limitations): https://learn.microsoft.com/microsoft-copilot-studio/add-inputs-prompt#limitations

Create a prompt (how inputs are defined): https://learn.microsoft.com/microsoft-copilot-studio/create-custom-prompt#create-a-new-prompt

Best regards,

Valantis

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📝 https://valantisond365.com/

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Valantis 3,240 on at

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Hi @SC-02030600-0,

Just wanted to check in and see if everything is working now. If you still need any help, feel free to let me know.

Also, if the issue is resolved, it would be great if you could mark the answer as solved so others with the same question can find it easily.

Thanks and have a great day!

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