[Fix] Include list index in multimodal validation error messages

[sjhddh]

Summary

Include the list index in multimodal validation error messages to help users identify which specific item has the issue.

Before:

Multi-modal data for image is None but UUID is not provided

After:

Multi-modal data for image[2] is None but UUID is not provided

Motivation

• Improves debuggability when working with batched multimodal inputs
• Makes it easier to identify which item in a list of images/videos/etc. is problematic

Test Plan

• Test with a list of multimodal inputs where one item is None without UUID
• Verify error message includes the correct index

Risk

• Very low risk: only changes error message string format
• No change to validation logic

[gemini-code-assist]

Code Review

This pull request improves error messages for multimodal validation by including the list index of the problematic item. This is a helpful change for debuggability. My review includes a suggestion to refactor the validation logic to improve its clarity, remove code duplication, and handle a potential edge case more robustly.

[gemini-code-assist]

While adding the index to the error message is a good improvement, this logic for checking missing UUIDs is duplicated and can be simplified. The nested if/else and repeated raise ValueError makes the code harder to read and maintain.

Additionally, there's a potential issue: the code assumes multi_modal_uuids[modality] is a list because isinstance(data, list) is true. However, if multi_modal_uuids[modality] were a string, len() would work but indexing would behave differently, potentially leading to incorrect validation.

Consider refactoring the entire if d is None: block to be more concise and robust, like this:

if d is None:
    uuid_provided = False
    if multi_modal_uuids is not None:
        modality_uuids = multi_modal_uuids.get(modality)
        if isinstance(modality_uuids, list) and i < len(modality_uuids) and modality_uuids[i] is not None:
            uuid_provided = True

    if not uuid_provided:
        raise ValueError(
            f"Multi-modal data for {modality}[{i}] is None "
            f"but UUID is not provided")

This refactoring consolidates the validation logic, removes duplication, and adds a check to ensure modality_uuids is a list, making it safer.

[DarkLight1337]

Thanks, but I'm actually working on revamping the validation in #32955