Minor improve:

+ ProgramPlayDialog rollback changes
+ DataWord all zeroes care

ethereumj-core/src/main/java/org/ethereum/gui/ContractCallDialog.java

@@ -357,7 +357,7 @@ class ContractCallDialog extends JDialog implements MessageAwareDialog{
                 WorldManager.instance.detaildDB.get(contractAddress);
 
         ContractDetails contractDetails = null;
-        if (contractDetailsB.length > 0)
+        if (contractDetailsB != null && contractDetailsB.length > 0)
             contractDetails = new ContractDetails(contractDetailsB);
 
         Transaction tx = createTransaction();

ethereumj-core/src/main/java/org/ethereum/gui/ProgramPlayDialog.java

@@ -51,13 +51,14 @@ public class ProgramPlayDialog extends JPanel implements ActionListener,
                 ProgramInvokeFactory.createProgramInvoke(tx, lastBlock, contractDetails,
                         trackDetailDB, trackChainDb, trackStateDB));
 
+        program.addListener(this);
+        program.fullTrace();
+        vm.play(program);
+
         trackDetailDB.rollbackTrack();
         trackChainDb.rollbackTrack();
         trackStateDB.rollbackTrack();
 
-        program.addListener(this);
-        program.fullTrace();
-        vm.play(program);
 
         setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
 

ethereumj-core/src/main/java/org/ethereum/util/ByteUtil.java

@@ -160,12 +160,14 @@ public class ByteUtil {
         if (data == null) return null;
 
         int firstNonZero = 0;
-        for (int i = 0; i < data.length; ++i)
+        int i = 0;
+        for (i = 0; i < data.length; ++i)
             if (data[i] != 0){
                 firstNonZero = i;
                 break;
             }
 
+        if (i == data.length) return new byte[1];
         if (firstNonZero == 0) return data;
 
         byte[] result = new byte[data.length - firstNonZero];