fix: 500 error after saving empty subsection release date

[DmytroAlipov]

Description

Steps to Reproduce:

1. In Studio create course -> on Course outline page add Section and Subsection

2. Click on three dots button for Subsections -> click on Configure

3. Set empty Release date, save changes

4. Watch the CMS logs:

2024-11-01 14:03:24,129 ERROR 403 [django.request] [user None] [ip None] log.py:241 - Internal Server Error: /xblock/outline/block-v1:RG+dimilitydiadimiljitydiadifnkffffffffffffffffffjkkkkkhhjllkn+2024+type@chapter+block@d51c801024ba44b8ac784375f6648723
Traceback (most recent call last):
  File "/openedx/venv/lib/python3.11/site-packages/django/core/handlers/exception.py", line 55, in inner
    response = get_response(request)
               ^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/venv/lib/python3.11/site-packages/django/core/handlers/base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/pyenv/versions/3.11.8/lib/python3.11/contextlib.py", line 81, in inner
    return func(*args, **kwds)
           ^^^^^^^^^^^^^^^^^^^
  File "/openedx/venv/lib/python3.11/site-packages/django/views/decorators/http.py", line 43, in inner
    return func(request, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/venv/lib/python3.11/site-packages/django/contrib/auth/decorators.py", line 23, in _wrapper_view
    return view_func(request, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/edx-platform/common/djangoapps/util/json_request.py", line 57, in parse_json_into_request
    return view_function(request, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/edx-platform/cms/djangoapps/contentstore/views/block.py", line 324, in xblock_outline_handler
    create_xblock_info(
  File "/openedx/venv/lib/python3.11/site-packages/edx_django_utils/plugins/pluggable_override.py", line 77, in wrapper
    return prev_fn(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/edx-platform/cms/djangoapps/contentstore/xblock_storage_handlers/view_handlers.py", line 982, in create_xblock_info
    child_info = _create_xblock_child_info(
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/edx-platform/cms/djangoapps/contentstore/xblock_storage_handlers/view_handlers.py", line 1520, in _create_xblock_child_info
    child_info["children"] = [
                             ^
  File "/openedx/edx-platform/cms/djangoapps/contentstore/xblock_storage_handlers/view_handlers.py", line 1521, in <listcomp>
    create_xblock_info(
  File "/openedx/venv/lib/python3.11/site-packages/edx_django_utils/plugins/pluggable_override.py", line 77, in wrapper
    return prev_fn(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/edx-platform/cms/djangoapps/contentstore/xblock_storage_handlers/view_handlers.py", line 998, in create_xblock_info
    visibility_state = _compute_visibility_state(
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/openedx/edx-platform/cms/djangoapps/contentstore/xblock_storage_handlers/view_handlers.py", line 1418, in _compute_visibility_state
    is_live = is_course_self_paced or datetime.now(UTC) > xblock.start
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: '>' not supported between instances of 'datetime.datetime' and 'NoneType'
[01/Nov/2024 14:03:24] "GET /xblock/outline/block-v1:RG+dimilitydiadimiljitydiadifnkffffffffffffffffffjkkkkkhhjllkn+2024+type@chapter+block@d51c801024ba44b8ac784375f6648723 HTTP/1.1" 500 340232

5. Comparison with legacy page

Because the string comes to the backend, the logic does not work correctly.

After fix:

[openedx-webhooks]

Thanks for the pull request, @DmytroAlipov!

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.27%. Comparing base (549dbaa) to head (f38eb0d).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1457   +/-   ##
=======================================
  Coverage   93.27%   93.27%           
=======================================
  Files        1052     1052           
  Lines       20465    20467    +2     
  Branches     4299     4384   +85     
=======================================
+ Hits        19089    19091    +2     
+ Misses       1316     1313    -3     
- Partials       60       63    +3     

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