[Jojoussef]

Description

Assigning DateRangeSlider.value = None raises a TypeError in _sync_values (panel/widgets/slider.py:785):

vs, ve = self.value
TypeError: cannot unpack non-iterable NoneType object

DateRangeSlider initializes with value = None when bounds are not yet supplied, and _process_param_change already handles value is None by deleting 'value' from model properties before sending them to Bokeh. However, _sync_values attempted to unpack self.value unconditionally whenever value changed.

This patch updates _sync_values to check whether self.value is None. When None, it updates value_start and value_end to None. When non-None, it unpacks the tuple as before. It also removes the unused allow_None=False argument on the param.DateRange declaration, which was overridden by Param because default=None.

Fixes #8871

I added two unit regression tests to panel/tests/widgets/test_slider.py:

• test_date_range_slider_value_none: verifies setting DateRangeSlider.value = None updates value_start and value_end to None without raising, and allows subsequent tuple re-assignment.
• test_datetime_range_slider_value_none: verifies the same behavior on DatetimeRangeSlider.

Both tests fail with TypeError on unchanged main and pass with this change. The complete slider test suite (pytest panel/tests/widgets/test_slider.py) passes with 84 passing tests.

Checklist

• Tests added and are passing

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.71%. Comparing base (cd9f377) to head (e93cb1b).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8901      +/-   ##
==========================================
- Coverage   89.79%   89.71%   -0.09%     
==========================================
  Files         406      406              
  Lines       69094    69118      +24     
==========================================
- Hits        62046    62011      -35     
- Misses       7048     7107      +59     

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