fix: Fix a bug while processing markdown file: 'str' object has no attribute 'get_ref'

[eai1111]

I've reached an unexpected crash while processing markdown (.md) files.

Stacktrace:

  File "/root/envs/eth/lib/python3.10/site-packages/docling/backend/md_backend.py", line 306, in iterate_elements
    self.iterate_elements(child, depth + 1, doc, parent_element)
  File "/root/envs/eth/lib/python3.10/site-packages/docling/backend/md_backend.py", line 306, in iterate_elements
    self.iterate_elements(child, depth + 1, doc, parent_element)
  File "/root/envs/eth/lib/python3.10/site-packages/docling/backend/md_backend.py", line 224, in iterate_elements
    doc.add_picture(parent=parent_element, caption=element.title)
  File "/root/envs/eth/lib/python3.10/site-packages/docling_core/types/doc/document.py", line 1602, in add_picture
    fig_item.captions.append(caption.get_ref())
AttributeError: 'str' object has no attribute 'get_ref'

Example data:

[![text](https://example.com "text")](https://example.com "text")

The caption is neither a text nor a ref item, it's a str. So get_ref should not be executed there.

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[dolfim-ibm]

The issue you report is actually a bug in the markdown backend. We have already a fix in place in a development PR which is going be released soon (like tomorrow).
https://github.com/DS4SD/docling/pull/752/files#diff-73af24b47bbe13d937125cc60da41fb12b2f8ec43f33c95f83385b9a67c5fca5L224

[eai1111]

awesome!

[dolfim-ibm]

I'm closing this PR, since the issue is addressed in the new Docling release.