Default value of 'pl.Array' typed attribute fails in graph.node_attrs()

[TeunHuijben]

When a node attribute has the type "Array", and I add a node without providing that attribute value (with validata_keys==False). A call to graph.node_attrs() gives the following error:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/teun.huijben/Documents/code/github/funtracks/.venv/lib/python3.12/site-packages/tracksdata/graph/_graph_view.py", line 625, in node_attrs
    return self._node_attrs_from_node_ids(attr_keys=attr_keys, unpack=unpack)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/teun.huijben/Documents/code/github/funtracks/.venv/lib/python3.12/site-packages/tracksdata/graph/_graph_view.py", line 609, in _node_attrs_from_node_ids
    node_dfs = super()._node_attrs_from_node_ids(
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/teun.huijben/Documents/code/github/funtracks/.venv/lib/python3.12/site-packages/tracksdata/graph/_rustworkx_graph.py", line 1102, in _node_attrs_from_node_ids
    s = pl.Series(name=key, values=columns[key], dtype=schema.dtype)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/teun.huijben/Documents/code/github/funtracks/.venv/lib/python3.12/site-packages/polars/series/series.py", line 306, in __init__
    self._s = sequence_to_pyseries(
              ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/teun.huijben/Documents/code/github/funtracks/.venv/lib/python3.12/site-packages/polars/_utils/construction/series.py", line 272, in sequence_to_pyseries
    if all(len(v) == n_elems for v in values):
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/teun.huijben/Documents/code/github/funtracks/.venv/lib/python3.12/site-packages/polars/_utils/construction/series.py", line 272, in <genexpr>
    if all(len(v) == n_elems for v in values):
           ^^^^^^
TypeError: object of type 'NoneType' has no len()

Coming from line 1102 in tracksdata/graph/_rustworkx_graph.py

        for key in attr_keys:
            schema = node_attr_schemas[key]
            s = pl.Series(name=key, values=columns[key], dtype=schema.dtype)
            s = _maybe_fill_null(s, schema)
            columns[key] = s