The onions are optional (frankly never heard of it being used Fleischsalad although it could give it a nice bite), pickle juice and sugar is just used flavor the mayo, salt and pepper to taste is standard for pretty much anything savory. The only REAL other ingredient here are the pickles.
So yes, Mr. German Police, you’re technically correct (of course), but I will count this as an off by one since you COULD just put the sausage, pickles, and mayo together and already have a decent approximation of the dish.