[TASK] Improve error message in base repository
[TASK] Improve error message in base repository

This makes an error message in Repository::update() more meaningful and
removes some obsolete code from the constructor.

Change-Id: I03c8b0a393fac5b41c3758ae99488032f3a6e17d
Original-Commit-Hash: 628780885d8035576a9618ab8733da30f22f9d37

dfeyer/flow-development-collection,fcool/flow-development-collection,chewbakartik/flow-development-collection,neos/flow-development-collection,fcool/flow-development-collection,neos/flow-development-collection,gerhard-boden/flow-development-collection,dfeyer/flow-development-collection,aertmann/flow-development-collection,mkeitsch/flow-development-collection,dfeyer/flow-development-collection,dlubitz/flow-development-collection,albe/flow-development-collection,gerhard-boden/flow-development-collection,dlubitz/flow-development-collection,dfeyer/flow-development-collection,kitsunet/flow-development-collection,fcool/flow-development-collection,kdambekalns/flow-development-collection,kdambekalns/flow-development-collection,chewbakartik/flow-development-collection,aertmann/flow-development-collection,dlubitz/flow-development-collection,kdambekalns/flow-development-collection,robertlemke/flow-development-collection,neos/flow-development-collection,kitsunet/flow-development-collection,chewbakartik/flow-development-collection,daniellienert/flow-development-collection,albe/flow-development-collection,kdambekalns/flow-development-collection,robertlemke/flow-development-collection,robertlemke/flow-development-collection,mkeitsch/flow-development-collection,mkeitsch/flow-development-collection,bwaidelich/flow-development-collection,aertmann/flow-development-collection,gerhard-boden/flow-development-collection,daniellienert/flow-development-collection,kitsunet/flow-development-collection,daniellienert/flow-development-collection,fcool/flow-development-collection,robertlemke/flow-development-collection,albe/flow-development-collection,bwaidelich/flow-development-collection,neos/flow-development-collection,bwaidelich/flow-development-collection