[BUGFIX] Catch None in image feature columns

[burtenshaw]

Description

This PR fixes this snippet:

import argilla as rg
from datasets import load_dataset

client = rg.Argilla(
    api_url="https://frascuchon-argilla.hf.space", api_key="argilla.apikey"
)

ds = load_dataset("derek-thomas/ScienceQA", name="default", split="train")
dataset = client.datasets(name="science_qa", workspace="argilla")

dataset.records.log(
    ds, mapping={"task": "text_0.suggestion", "subject": "text_1.suggestion"}
)

Closes #<issue_number>

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (change restructuring the codebase without changing functionality)
• Improvement (change adding some improvement to an existing functionality)
• Documentation update

How Has This Been Tested

Checklist

• I added relevant documentation
• I followed the style guidelines of this project
• I did a self-review of my code
• I made corresponding changes to the documentation
• I confirm My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have added relevant notes to the CHANGELOG.md file (See https://keepachangelog.com/)