code: def test_union_sort_other_empty_sort():
      idx = MultiIndex.from_product([[1, 0], ["a", "b"]])
      other = idx[:0]
      result = idx.union(other, sort=True)
      expected = MultiIndex.from_product([[0, 1], ["a", "b"]])
      tm.assert_index_equal(result, expected)
  
imports: import numpy
  import pytest
  import pandas
  from pandas import CategoricalIndex, DataFrame, Index, IntervalIndex, MultiIndex, Series
  import pandas._testing
  from pandas.api.types import is_float_dtype, is_unsigned_integer_dtype
label_desc: Use image node_id 21 for calling a global function with example usage: test_union_sort_other_empty_sort() without return types