XO0406: operator, index, slice, or iteration not defined for the type

The operation does not exist for this type: arithmetic between Duration and a plain integer literal, Time + Time, indexing a Str by position, slicing something other than List, Bytes, or Str, for over a value that is not a List, Set, Map, Chan, Bytes, or range, ?? on a non optional, or expect(x) without a comparison. Durations need units (5s), and a Str is read with runes() or by slicing. See core 2.1, 3.5, and 3.6.

Example

fn f(d: Duration) -> Duration { d + 5 }

Fix

fn f(d: Duration) -> Duration { d + 5s }

Run xo explain XO0406 for this text in a terminal, or see section 10.6 of the specification.