code: def testEmpty(self):
      lag = PercivalEvaluatePulseTrains()([], [])
      self.assertEqual(-1.0, lag)
  
file_path: essentia/test/src/unittests/rhythm/test_percivalevaluatepulsetrains.py
imports: from essentia_test import *
  from essentia.standard import MonoLoader, PercivalEvaluatePulseTrains, HarmonicBpm, FrequencyBands, NoveltyCurve
label_desc: Use image node_id 1 for calling the TestPercivalEvaluatePulseTrains obj's underlying member method code with example usage: obj.testEmpty() without return types