Using clear on Series of type Object results in dtype Null when first value is null

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Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

import polars as pl

s = pl.Series([None, object()])
result = s.clear()
print(result)

Log output

shape: (0,)
Series: '' [null]
[
]

Issue description

Problematic code is here:

polars/crates/polars-core/src/series/mod.rs

Lines 166 to 167 in 9f1b08f

	let av = self.get(0).unwrap();
	Series::new(self.name(), [av]).slice(0, 0)

The first value is taken to infer the data type, while the first non-null value should be taken.

Expected behavior

Result in Series with Object data type.

Installed versions

main