Version: latest (3.21.7 in particular, but it's in git)
Langauge: java

ByteString.java does not currently specify a serialVersionUID. This is wreaking havoc on countless places that include byte strings in their serialization format. For example, the google-cloud-datastore Entity class is serializable and frequently serialized into memcache-like services, but it composes ByteString so serialization breaks with different versions of the protobuf jar.

Some of the subclasses specify serialVersionUID which is great, but the base class needs to as well. Looks like an oversight.