safer copy constructor

diff --git a/src/jalview/datamodel/DBRefEntry.java b/src/jalview/datamodel/DBRefEntry.java
index 7491da2..b6c3192 100755 (executable)
--- a/src/jalview/datamodel/DBRefEntry.java
+++ b/src/jalview/datamodel/DBRefEntry.java
@@ -47,7 +47,10 @@ public class DBRefEntry
   }
   public DBRefEntry(DBRefEntry entry)
   {
-    this(new String(entry.source), new String(entry.version), new String(entry.accessionId), new Mapping(entry.map));
+    this((entry.source==null ? "" : new String(entry.source)), 
+            (entry.version==null ? "" : new String(entry.version)),
+            (entry.accessionId==null ? "" : new String(entry.accessionId)),
+            (entry.map==null ? null : new Mapping(entry.map)));
   }
   public boolean equals(DBRefEntry entry) {
       if (entry==this)