1) testPutIfAbsent, testRemoveIfPresent, testReplaceWithOldVal (methods
the test cases)
In this tests, it was updating the cache entry with a null version. This
originates later a IllegalStateException when it tries to perform the
write skew check and the version is null.
I have fixed this problem in this way: if the command fails (PutCommand,
RemoveCommand, ReplaceCommand), I unset the flag CHANGED in the
MvccEntry to avoid to update the entry in the DataContainer.
2) testClear in distributed mode
I have no clear idea how to solve this problem but it looks like the
PrepareCommand (with the ClearCommand) is not sent to all the nodes in
the cluster. Then, when I do a get, a remote get is performed and the
key is still there. I think that it is not the desired behavior.
In this test, it tries to remove a key that does not exists but it does
not success due to a NullPointerException. I have looked deeper and I
check that the transaction's lookup entries map has an entry with [key
=> null] and when it tries to perform the write skew check in that key,
a NullPointerException is thrown in here  (line 80, WriteSkewHelper)