I belive you have misread the first line of the method. You see it's setting AuthorInitials to aString not AuthorName.

The complete code for the method is:

setAuthorInitials: aString

AuthorInitials _ aString.

"Case of being reset due to, eg, copy of image." aString isEmpty ifTrue: [AuthorName _ ''] aString isEmpty ifTrue: [AuthorName _ nil]