Encrypting my session key with a certificate present in memory only, not on hard drive

[p m]

Hello,
I don't know how i can encrypt and decrypt a SOAP message with a certificate present in memory only (generate dynamicaly) and not on hard drive.

I can encrypt without any problems.
I have an error (NullPointeurException) when i try to decrypt my SOAP message.
The NullPointeurException is because the "property" of my org.apache.ws.security.components.crypto.AbstractCrypto is set to "null" and there is a call to the method getCertificateFactory() :
String provider = properties.getProperty("org.apache.ws.security.crypto.merlin.cert.provider");

In the constructor of the same AbstractCrypto (called by AbstractCrypto c = CryptoFactory.getInstance('org.apache.ws.security.components.crypto.Merlin ', (Properties)null), there is this test and comments :
        /*
        * if no properties .. just return an instance, the rest will be
        * done later or this instance is just used to handle certificate
        * conversions in this implementatio
        */
        if (properties == null) {
            return;
        }

Is there a problem with the decryption method when the Crypto have his property setting to 'null'?

Thanks for your help, i really don't what can i do to resolve my problem.
Matthieu