code: def test_replace_nulls(gsr, old, new, expected):
      actual = gsr.replace(old, new)
      assert_eq(
          expected.sort_values().reset_index(drop=True),
          actual.sort_values().reset_index(drop=True),
      )
  
imports: import re
  from decimal import Decimal
  import numpy
  import pandas
  import pytest
  import cudf
  from cudf.core._compat import PANDAS_GE_134, PANDAS_GE_150
  from cudf.core.dtypes import Decimal32Dtype, Decimal64Dtype, Decimal128Dtype
  from cudf.testing._utils import INTEGER_TYPES, NUMERIC_TYPES, assert_eq, assert_exceptions_equal
label_desc: Use image node_id 32 for calling a global function with example usage: test_replace_nulls(gsr, old, new, expected) without return types