fix: always define a student_data_store to prevent errors on XBlock load [FC-0076]

[rpenido]

Description

This PR adds a DictFieldData to the student_data_store if the user is not defined.

Additional Information

More info here: openedx/XBlock#815 (comment)

This fixes an error on the meilisearch index update after saving the Survey Xblock.

cms-1          | 2025-01-28 19:36:18,402 ERROR 2163 [celery_utils.logged_task] [user 4] [ip 172.18.0.1] logged_task.py:48 - [9d7cda4b-afd2-404f-a39c-7a185c486907] failed due to Traceback (most recent call last):
cms-1          |   File "/openedx/venv/lib/python3.11/site-packages/celery/app/trace.py", line 453, in trace_task
cms-1          |     R = retval = fun(*args, **kwargs)
cms-1          |                  ^^^^^^^^^^^^^^^^^^^^
cms-1          |   File "/openedx/venv/lib/python3.11/site-packages/celery/app/autoretry.py", line 38, in run
cms-1          |     return task._orig_run(*args, **kwargs)
cms-1          |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cms-1          |   File "/openedx/venv/lib/python3.11/site-packages/edx_django_utils/monitoring/internal/code_owner/utils.py", line 195, in new_function
cms-1          |     return wrapped_function(*args, **kwargs)
cms-1          |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cms-1          |   File "/openedx/edx-platform/openedx/core/djangoapps/content/search/tasks.py", line 57, in upsert_library_block_index_doc
cms-1          |     api.upsert_library_block_index_doc(usage_key)
cms-1          |   File "/openedx/edx-platform/openedx/core/djangoapps/content/search/api.py", line 639, in upsert_library_block_index_doc
cms-1          |     searchable_doc_for_library_block(library_block_metadata)
cms-1          |   File "/openedx/edx-platform/openedx/core/djangoapps/content/search/documents.py", line 381, in searchable_doc_for_library_block
cms-1          |     block = xblock_api.load_block(xblock_metadata.usage_key, user=None)
cms-1          |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cms-1          |   File "/openedx/edx-platform/openedx/core/djangoapps/xblock/api.py", line 117, in load_block
cms-1          |     return runtime.get_block(usage_key, version=version)
cms-1          |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cms-1          |   File "/openedx/edx-platform/openedx/core/djangoapps/xblock/runtime/learning_core_runtime.py", line 229, in get_block
cms-1          |     block.force_save_fields(block._get_fields_to_save())  # pylint: disable=protected-access
cms-1          |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
cms-1          |   File "/mnt/xblock/xblock/core.py", line 531, in force_save_fields
cms-1          |     self._field_data.set_many(self, fields_to_save_json)
cms-1          |   File "/mnt/xblock/xblock/field_data.py", line 164, in set_many
cms-1          |     field_data.set_many(block, new_update_dict)
cms-1          |     ^^^^^^^^^^^^^^^^^^^
cms-1          | AttributeError: 'NoneType' object has no attribute 'set_many'

The underlying issue is that the mutable fields are written on XBlock load, even if they are from user_state scope, as in the example of the Survey XBlock above:

cms-1          | block._get_fields_to_save() ['feedback', 'max_submissions', 'private_results', 'answers', 'block_name', 'choices', 'display_name', 'questions']

As the LearningCoreXBlockRuntime doesn't had the Scope.user_state before, the get_block function throws an error.

Testing instructions

• Edit a Survey block on the Library Authoring page and check the error above
• Checkout the current PR and mount it on your tutor stack
• Check that the error is gone and the block document is updated successfully

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Private ref: FAL-4033

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[pomegranited]

👍 Works for me, thank you @rpenido !

Do we need to bump the XBlock dependency too?

• I tested this with fix: throw an error if the scope if None on scope_mappings [FC-0076] XBlock#815 using the PR test instructions.
• I read through the code
• I checked for accessibility issues N/A
• Includes documentation N/A
• User-facing strings are extracted for translation N/A