diff -u -r1.5 -r1.6
--- PerfectIdentifier.java	11 Feb 2007 17:12:12 -0000	1.5
+++ PerfectIdentifier.java	16 May 2007 17:30:21 -0000	1.6
@@ -14,7 +14,7 @@

 
 /**
  * 

- * @version $Id: PerfectIdentifier.java,v 1.5 2007/02/11 17:12:12 cassell Exp $

+ * @version $Id: PerfectIdentifier.java,v 1.6 2007/05/16 17:30:21 mcharles Exp $

  */
 
 public class PerfectIdentifier extends Driver

@@ -35,6 +35,38 @@

 	for (Cluster clus : inputClusterList) {
 	    // Identify
 	    MCParticle truthID = findTruthID(clus, mcList);

+	    if (truthID == null) {
+		// This is going to cause a null pointer exception shortly
+		// (as soon as we try to compute the truth particle's
+		// energy, momentum, etc). So pre-emptively throw a diagnostic
+		// exception.
+		String printme = new String();
+		printme += ("Warning: truthID==null for cluster with "+clus.getCalorimeterHits().size()+" hits and MC list of "+mcList.size()+" particles named '"+m_mcName+"'.\n");
+		printme += "Probably the MC list is not complete or is not self-consistent.\n";
+		printme += "Here are the contributing particles:\n";
+		Set<MCParticle> contributingParticles  = new HashSet<MCParticle>();
+		for (CalorimeterHit hit : clus.getCalorimeterHits()) {
+		    SimCalorimeterHit simHit = (SimCalorimeterHit) (hit);
+		    int nContributingParticles = simHit.getMCParticleCount();
+		    for (int i=0; i<nContributingParticles; i++) {
+			MCParticle part = simHit.getMCParticle(i);
+			contributingParticles.add(part);
+		    }
+		}
+		for (MCParticle part : contributingParticles) {
+		    List<MCParticle> parentsInList = findParentsInList(part, mcList);
+		    printme += "    ";
+		    printme += part.getType().getName();
+		    printme += " with energy "+part.getEnergy();
+		    printme += " with parents in list: { ";
+		    for (MCParticle parent : parentsInList) {
+			printme += parent.getType().getName();
+			printme += "(E="+parent.getEnergy()+") ";
+		    }
+		    printme += " } \n";
+		}
+		throw new NullPointerException(printme);
+	    }

 	    // Add to output list
 	    LocalReconstructedParticle part = new LocalReconstructedParticle();
 	    part.addCluster(clus);