* allow 3.4 behaviour regarding aggregate collect and undefined variable
* added test to check undefined var
* rm print
* remove duplicate doCopyRow
* wrongly removed due merge
* initialize _allowSourceRowUninitialized always as false as default
* try to fix another case
* added missing parenthesis
* optimized if, also added compiler hint
* Removed useless parameters of buildCallback
* Renamed produceRow to produceRows and adapted a comment
* Renamed BlockFetcher to DependencyProxy
* Applied git-clang-format