code: def test_trio_matrix_null_keys(self):
      ped = hl.Pedigree.read(resource("triomatrix.fam"))
      ht = hl.import_fam(resource("triomatrix.fam"))
  
      mt = hl.import_vcf(resource("triomatrix.vcf"))
      mt = mt.annotate_cols(fam=ht[mt.s].fam_id)
  
      # Make keys all null
      mt = mt.key_cols_by(s=hl.missing(hl.tstr))
  
      tt = hl.trio_matrix(mt, ped, complete_trios=True)
      self.assertEqual(tt.count_cols(), 0)
  
imports: import unittest
  import hail
  from ..helpers import *
label_desc: Use image node_id 3 for calling the Tests obj's underlying member method code with example usage: obj.test_trio_matrix_null_keys() without return types