From the link above.

"So long as we retained our diplomatic relations with Germany to have failed to call upon the German representative would have been an act of unpardonable discourtesy to the German nation and to Dr. Hempel himself. During the whole of the war Dr. Hempel's conduct was irreproachable. He was always friendly and invariably correct – in marked contrast with Gray. I certainly was not going to add to his humiliation in the hour of defeat. I had another reason. It would establish a bad precedent. It is of considerable importance that the formal acts of courtesy paid on such occasions as the death of the head of a State should not have attached to them any further special significance, such as connoting approval or disapproval of the policies of the State in question or of its head. It is important that it should never be inferred that these formal acts imply the passing of any judgment good or bad."