WARNING: RAR5038:Unexpected exception while creating resource for pool connectionPoolAlunnoWS.

Hi, I'm an Italian student and unfortunately I do not speak English well yet. I write to you using google translator to optimize the time: D
I have the following problem:

WARNING: RAR5038: Unexpected exception while creating resource for pool connectionPoolAlunnoWS. Exception: javax.resource.spi.ResourceAllocationException: Connection could not be allocated Because:

FATAL: database "null" does not exist

I use Netbeans 7.3 + Glassfish + postgresql, I am developing a web service and I was following the tutorial where it uses EJB and jax-ws Your text to link...
I followed all the steps but I have this problem during deployment.

under Services -> databases I created the connection by selecting the driver for postgresql and the test connection is ok.
I run the JDBC connection pool and then I run JDBC Resource as a tutorial.
I tried, again, to follow the tutorial from the beginning. The problem is always the same.

Please help me!

P.S:
I attach one screenshot of the error.
sorry again for my English. XD