code: def get_existence(self):
      for case in (
          self.test_empty,
          self.test_full,
          self.reference_empty,
          self.reference_full,
      ):
          if case is None:
              self.compute()
              break
  
      return (
          self.test_empty,
          self.test_full,
          self.reference_empty,
          self.reference_full,
      )
  
imports: import numpy
  from medpy import metric
label_desc: Use image node_id 8 for calling the ConfusionMatrix obj's underlying member method code with example usage: obj.get_existence() and returns: self,  self,  self,  self