[Python] Keep only rows that have atleast one null

I am trying to do basically the opposite of drop_nulls(). I want to keep all rows that have at least one null.

I want to do something like (but I don't want to list all other columns):

for (name,) in (
df.filter(
pl.col("a").is_null()
| pl.col("b").is_null()
| pl.col("c").is_null()
)
.select("name")
.unique()
.rows()
):
print(
f"Ignoring `{name}` because it has at least one null",
file=sys.stderr,
)
df = df.drop_nulls()

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