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


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


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

# create a context
ctx = SessionContext()

# create a RecordBatch and a new DataFrame from it
batch = pa.RecordBatch.from_arrays(
    [pa.array([1, 2, 3]), pa.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) == pa.array([False] * 3)