reset_index behavior on empty frames

[delucchi-cmu]

Bug report

See debugging in the following notebooks:

https://github.com/lincc-frameworks/notebooks_lf/blob/main/sprints/2025/12_04/issue_994.ipynb

reset_index behaves differently for empty vs populated dataframes under <hand-waving>SOME</hand-waving> conditions.

Environment Information

lsdb 0.7.1
nested 0.6.2

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[delucchi-cmu]

More info:

>> new_m_f = nf_m.reset_index().set_index("objectid")
>> new_m_f.index.name

'objectid'

>> new_m_f = nf_m.reset_index().set_index("objectid").nest_lists(columns=['hmjd', 'mag', 'magerr', 'catflags', 'clrcoeff'],name="lc")
>> new_m_f.index.name

<nothing>

So the NAME of the index is dropped when the dataframe is empty.

[hombit]

I believe it happened here, and we should just set the index name

nested-pandas/src/nested_pandas/nestedframe/core.py

Lines 688 to 691 in 464bffa

	if len(df) == 0:
	# if the dataframe is empty, just return an empty nested column
	# since there are no iterable values to pack
	packed_df = NestedFrame().join_nested(df[list_columns], name=name)