split the getTransaction() method

I don't like methods that do something completely different with a null parameter

h2/src/main/org/h2/mvstore/db/MVPrimaryIndex.java

@@ -66,7 +66,7 @@ public class MVPrimaryIndex extends BaseIndex {
         ValueDataType valueType = new ValueDataType(db.getCompareMode(), db,
                 sortTypes);
         mapName = "table." + getId();
-        Transaction t = mvTable.getTransaction(null);
+        Transaction t = mvTable.getTransactionBegin();
         dataMap = t.openMap(mapName, keyType, valueType);
         t.commit();
         if (!table.isPersistData()) {

h2/src/main/org/h2/mvstore/db/MVSecondaryIndex.java

@@ -67,7 +67,7 @@ public class MVSecondaryIndex extends BaseIndex implements MVIndex {
         ValueDataType keyType = new ValueDataType(
                 db.getCompareMode(), db, sortTypes);
         ValueDataType valueType = new ValueDataType(null, null, null);
-        Transaction t = mvTable.getTransaction(null);
+        Transaction t = mvTable.getTransactionBegin();
         dataMap = t.openMap(mapName, keyType, valueType);
         t.commit();
         if (!keyType.equals(dataMap.getKeyType())) {

h2/src/main/org/h2/mvstore/db/MVSpatialIndex.java

@@ -102,7 +102,7 @@ public class MVSpatialIndex extends BaseIndex implements SpatialIndex, MVIndex {
                 new MVRTreeMap.Builder<VersionedValue>().
                 valueType(valueType);
         spatialMap = db.getMvStore().getStore().openMap(mapName, mapBuilder);
-        Transaction t = mvTable.getTransaction(null);
+        Transaction t = mvTable.getTransactionBegin();
         dataMap = t.openMap(spatialMap);
         t.commit();
     }

h2/src/main/org/h2/mvstore/db/MVTable.java

@@ -846,16 +846,22 @@ public class MVTable extends TableBase {
     }
 
     /**
-     * Get the transaction to use for this session.
+     * Get a new transaction.
      *
-     * @param session the session
      * @return the transaction
      */
-    Transaction getTransaction(Session session) {
-        if (session == null) {
+    Transaction getTransactionBegin() {
         // TODO need to commit/rollback the transaction
         return transactionStore.begin();
     }
+
+    /**
+     * Get the transaction to use for this session.
+     *
+     * @param session the session
+     * @return the transaction
+     */
+    Transaction getTransaction(Session session) {
         return session.getTransaction();
     }