NPE if using CachingMostRecentProvider to decrypt records without "amzn-ddb-meta-id"

[lavaleri]

Problem:

If a user attempts to use a CachingMostRecentProvider to decrypt a record that does contain a mat-desc, but that mat-desc does not contain the key value "amzn-ddb-meta-id," they get an NPE. This can happen if a user tries to encrypt with another one of our providers then decrypt with the CachingMostRecentProvider.

Solution:

Instead, users should get a more friendly error that decryption was unable to succeed.

Out of scope:

The CachingMostRecentProvider is not intended to interoperate with other providers.