fix ModelEncryptionSupport serializer/deserializer

[hlavki]

DefaultEncryptingOAuthDataProvider is practically unusable because serialization errors in ModelEncryptionSupport:

1. new Client("clientId", null, false) was serialized as with space as secret. So when the client was deserialized, then secretId was ' ' instead of null.
2. All collections were serialized with space e.g. "openid, email" then deserialized values with spaces: 'openid', ' email'

This patch provides fixes for this behavior.