An unknown perpetrator set off a stink bomb during an appearance by German Finance Minister Christian Lindner at the OMR Festival digital trade fair in Hamburg on Wednesday. A foul odour spread within minutes through the large hall which can hold around 7,000 people. A medical service checked the stink bomb, determined that it was not butyric acid and classified it as harmless to health, an OMR spokeswoman in Hamburg said. The hall was aired out immediately afterwards and the fire brigade did not have to be called. The perpetrator had not yet been identified, the spokeswoman said. The organize…