Fix: Guard against None num_query_tokens in Blip2Processor (to avoid TypeError)

[Flakes342]

What does this PR do?

Fixes #42203

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Fixed a bug where Blip2Processor assumes num_query_tokens is an int and does max_length - self.num_query_tokens which raises TypeError when num_query_tokens is None.

This change:

• Treats num_query_tokens as 0 when it is None (with a warning).
• Adds a minimal unit test to prevent regression.

Who can review?

@Rocketknight1

[Rocketknight1]

cc @zucchini-nlp! I think it's fine without the warning message, but deferring to her on what behaviour we want from processors 😅

[zucchini-nlp]

@Flakes342 thanks for the PR!

To support older models from the hub which weren't updated, I think we should update the default value of num_query_tokens.

The modeling code assumes that input_ids have special image placeholders and with self.num_query_tokens=None the placeholders will not be added in the input text. Therefore the model will not see an input image

Let's add the default value of 32 which is the only value used in all official checkpoints. Ping me for another review when ready :)

[HuggingFaceDocBuilderDev]

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[Flakes342]

@zucchini-nlp thr pr is ready for your review

[github-actions]

[For maintainers] Suggested jobs to run (before merge)

run-slow: blip_2

[zucchini-nlp]

run-slow: blip_2

[zucchini-nlp]

Sorry if I wasn't clear, I meant the default value in the signature here

[github-actions]

This comment contains run-slow, running the specified jobs:

models: ["models/blip_2"]
quantizations: []

[github-actions]

CI Results

Workflow Run ⚙️

Model CI Report

❌ Failed tests

• blip_2:
  tests/models/blip_2/test_modeling_blip_2.py::Blip2ModelIntegrationTest::test_inference_itm
  tests/models/blip_2/test_modeling_blip_2.py::Blip2ModelIntegrationTest::test_inference_itm_fp16