code: def test_fss_empty_results():
      fss = FastStreamlineSearch(
          f1,
          max_radius=2.0,
          nb_mpts=2,
          bin_size=20.0,
          resampling=22,
          bidirectional=True,
      )
      res = fss.radius_search(f2, radius=0.01, use_negative=True)
      assert_true(res.nnz == 0)
  
file_path: dipy/dipy/segment/tests/test_fss.py
imports: import numpy
  from dipy.data import get_fnames
  from dipy.io.streamline import load_tractogram
  from dipy.segment.fss import FastStreamlineSearch, nearest_from_matrix_row, nearest_from_matrix_col
  from dipy.segment.metric import mean_euclidean_distance
  from dipy.testing import assert_arrays_equal, assert_greater, assert_greater_equal, assert_true
  from numpy.testing import assert_almost_equal, assert_raises
label_desc: Use image node_id 5 for calling a global function with example usage: test_fss_empty_results() without return types