map_elements replaces all array elements with nulls about polars HOT 1 OPEN

pl.DataFrame({"a": [1, 2, 3]}).with_columns(pl.all().map_elements(
    {1: [None], 2: [9.0], 3: [10.0]}.get,
    return_dtype=pl.List(pl.Float64)
))
# shape: (3, 1)
# ┌───────────┐
# │ a         │
# │ ---       │
# │ list[f64] │
# ╞═══════════╡
# │ [null]    │
# │ [null]    │ # ???
# │ [null]    │ # ???
# └───────────┘

pl.DataFrame({"a": [1, 2, 3]}).with_columns(pl.all().map_elements(
    {1: [9.0], 2: [None], 3: [10.0]}.get,
    return_dtype=pl.List(pl.Float64)
))
# shape: (3, 1)
# ┌───────────┐
# │ a         │
# │ ---       │
# │ list[f64] │
# ╞═══════════╡
# │ [9.0]     │
# │ [null]    │
# │ [10.0]    │
# └───────────┘