message: Protection against null pointer to TParticle
diff: @@ -461,6 +461,7 @@ void AliAnalysisTrackingUncertaintiesAOT::ProcessTracks(AliStack *stack) {
  track->GetImpactParameters(dca, cov);
  if(fMC){
  part = (TParticle*)stack->Particle(TMath::Abs(track->GetLabel()));
  + if(part){
  pdgPart = part->GetPDG();
  code = pdgPart->PdgCode();
  if(stack->IsPhysicalPrimary(TMath::Abs(track->GetLabel()))) isph=1;
  @@ -487,6 +488,7 @@ void AliAnalysisTrackingUncertaintiesAOT::ProcessTracks(AliStack *stack) {
  if(TMath::Abs(code)==321) specie = 2;
  if(TMath::Abs(code)==2212) specie = 3;
  }
  + }
  //
  // relevant variables
  //
  