PaliGemma - fix processor with no input text

[hiyouga]

What does this PR do?

Fix the paligemma processor raises exception on empty text inputs

Reproduce

from PIL import Image
from transformers import AutoProcessor

image = Image.new("RGB", (100, 100), (255, 255, 255))
processor = AutoProcessor.from_pretrained("google/paligemma-3b-pt-224")
processor(images=image)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/lib/python3.10/site-packages/transformers/models/paligemma/processing_paligemma.py", line 190, in __call__
    pass
TypeError: 'NoneType' object is not iterable

The following lines require text should be a list, we need to convert the Nonetype input to a string or list firstly.

transformers/src/transformers/models/paligemma/processing_paligemma.py

Lines 176 to 179 in 92d1d97

	if text is None:
	logger.warning_once(
	"You are using PaliGemma without a text prefix. It will perform as a picture-captioning model."
	)

transformers/src/transformers/models/paligemma/processing_paligemma.py

Lines 186 to 198 in 92d1d97

	if _is_str_or_image(text):
	text = [text]
	elif isinstance(text, list) and _is_str_or_image(text[0]):
	pass
	input_strings = [
	build_string_from_input(
	prompt=prompt,
	bos_token=self.tokenizer.bos_token,
	image_seq_len=self.image_seq_length,
	image_token=IMAGE_TOKEN,
	)
	for prompt in text
	]

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

@amyeroberts

[amyeroberts]

cc @molbap

[molbap]

Hi @hiyouga , thanks for the fix! LGTM

[molbap]

LGTM

[amyeroberts]

Thanks for fixing!

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.