How to fix “Deserialization Not Allowed For Class” Error during AEM upgrade?

Let us see, How to solve “Deserialization Not Allowed For Class” Error during AEM upgrade.

When does this AEM upgrade issue occur?

While performing the upgrade, one of the custom codes started throwing an error, where it was using
java.security.KeyStore and trying to load the KeyStore, The error is as mentioned below –

com.package.core.exception.SystemException: java.lang.UnsupportedOperationException: Deserialization not allowed for class com.sun.crypto.provider.SealedObjectForKey

How to resolve this AEM Upgrade Issue?

To resolve this error, the com.sun.crypto.provider.SealedObjectForKey deserialization was added to the whitelisted classes list in the deserialization firewall configuration.