What product/version are you running? I see that this is coming out of a call to DatabaseImpl.save() which comes from step 4 of unlockrulesetversion. I jumped on a system I have laying around (Pega CS for Insurance 7.3.1) and don't see a save at step 4. But the activity unlockrulesetversion only exists in the PegaInsure ruleset in my system, so I don't think this is a platform rule at all, so my reference system may not be at all relevant if you are seeing this from a different application. Looking at the rest of the stack, the NPE is in the stream encoder, which I'm guessing is what generates the pzpvstream (i.e. the blob). Is this object that you are saving one that has a blob column? If not, that could perhaps account for it? I'd take a hard look at what you are saving. If you do a similar obj-save from a custom activity once that object is on the clipboard, do you see the same error? Something different? What about for other objects? Is this a work object, some data, or something else entirely?