Question about usage of Predicate.struct with optional properties

declare const valueWithProp: { name: string | number };

[valueWithProp]
  .filter(Predicate.struct({ name: Predicate.isString })) // ok
  .map(result => result); // resulting type => { name: string }

declare const valueWithOptionalProp: { name?: string | number };

[valueWithOptionalProp]
  .filter(Predicate.struct({ name: Predicate.isString })) // compile error
  .map(result => result); // resulting type => { name: string }