CASE

Conditional expressions can be expressed in the Cypher language with the CASE expression. A simple form is used to compare an expression against multiple predicates. For the first matched predicate result of the expression provided after the THEN keyword is returned. If no expression is matched value following ELSE is returned is provided, or null if ELSE is not used:

MATCH (n)
RETURN CASE n.currency WHEN "DOLLAR" THEN "$" WHEN "EURO" THEN "€" ELSE "UNKNOWN" END;

In generic form, you don't need to provide an expression whose value is compared to predicates, but you can list multiple predicates and the first one that evaluates to true is matched:

MATCH (n)
RETURN CASE WHEN n.height < 30 THEN "short" WHEN n.height > 300 THEN "tall" END;

Most expressions that take null as input will produce null. This includes boolean expressions that are used as predicates. In this case, anything that is not true is interpreted as being false. This also concludes that logically null!=null.