3 // NullVal returns a null value of the given type. A null can be created of any
4 // type, but operations on such values will always panic. Calling applications
5 // are encouraged to use nulls only sparingly, particularly when user-provided
6 // expressions are to be evaluated, since the precence of nulls creates a
7 // much higher chance of evaluation errors that can't be caught by a type
9 func NullVal(t Type) Value {