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import pyarrow
from datafusion import udf, SessionContext, functions as f


def is_null(array: pyarrow.Array) -> pyarrow.Array:
    return array.is_null()


is_null_arr = udf(is_null, [pyarrow.int64()], pyarrow.bool_(), "stable")

# create a context
ctx = SessionContext()

# create a RecordBatch and a new DataFrame from it
batch = pyarrow.RecordBatch.from_arrays(
    [pyarrow.array([1, 2, 3]), pyarrow.array([4, 5, 6])],
    names=["a", "b"],
)
df = ctx.create_dataframe([[batch]])

df = df.select(is_null_arr(f.col("a")))

result = df.collect()[0]

assert result.column(0) == pyarrow.array([False] * 3)