Twenty-five years ago, the cartoon strip “Mutts” debuted. It was the dream job for Patrick McDonnell, who had already enjoyed a career as an illustrator. The Art of Nothing is a beautifully rendered career retrospective, encompassing many pages of “Mutts” along with book and newspaper illustrations and early prototypes. The adventures of a companionable dog and cat, “Mutts” harkens back to such early 20th-century cartoon strips as the “Katzenjammer Kids” with its simple but expressive lines and to Japanese woodblocks for its use of blank space. McDonnell’s ideas are compact and clever, ideal for their medium and suffused with a love for all living things.