code: func (t *Trainer) pretrainCheck() error {
  	// check
  	if t.nn == nil || !t.nn.initialized() {
  		return errors.Errorf("DependencyParser not init()'d. Perhaps you forgot to call .Init() somewhere?")
  	}
  
  	if len(t.trainingSet) == 0 {
  		return errors.Errorf("Cannot train with no training data set")
  	}
  
  	return nil
  }
docs: // pretrainCheck checks if everything is sane