Germany 'reveals secret agreement' with Poland on migrants? Multi-stage manipulation

"The Germans have spilled the beans", "the mystery of Bundeswehr cars has been solved" - net users comment on the information that the German government "revealed a secret agreement" from 2014. Allegedly, it allows migrants to be smuggled out of Germany without Polish consent. This is not true, and it is spread by a well-known activist of the youth organization of the Law and Justice party.