code: def test_update_columnar_partial_unset(self):
      tbl = Table(
          [{"a": "abc", "b": 1, "c": 2}, {"a": "def", "b": 3, "c": 4}],
          index="a",
      )
  
      tbl.update({"a": ["abc"], "b": [None]})
  
      assert tbl.view().to_records() == [
          {"a": "abc", "b": None, "c": 2},
          {"a": "def", "b": 3, "c": 4},
      ]
  
imports: import numpy
  import pyarrow
  import pandas
  from datetime import date, datetime
  from perspective.table import Table
  from pytest import mark
label_desc: Use image node_id 13 for calling the TestUpdate obj's underlying member method code with example usage: obj.test_update_columnar_partial_unset() without return types