Add: [A.] [2.]A.2 c.A.2.c Math. Of a set: *containing no elements;* = null a. 4 c. Also applied transf. to other entities, esp. in Computing. *Opp. *non-empty a.*
1937 Jrnl. Symbolic Logic II. 67 A set or class *is said to be empty if there is no element of it.* 1946 A. Weil Found. Algebraic Geom. iv. 84 The bunch of varieties defined by an empty set of varieties will be called empty. 1966 [see injective a.]. 1981 A. Chandor Penguin Dict. Microprocessors 130 Null string, a string with no characters. *Also known as empty string.*

—OED