I understand your difficulty! But I can confirm that the first example is correct, and the second is possible. In the first case, we know what sort of courage that was lacking, namely the particular type of courage coming from one's convictions. In the second case one could say "lacking the courage, he never spoke to her." By saying "Lacking courage", the author is implying that Hitler lacked all courage, or that he did not have enough courage of any sort for the task.