Optional fields affecting keyof operator in generic class decorators

**TypeScript Version:** 3.2.2 <!-- Search terms you tried before logging this (so others can find this issue more easily) --> **Search Terms:** class decorator keyof typescript **Code** ```ts function View<T>(name: string, fields: (keyof T)[]) { return (target: new(...args: any[]) => T) => { // Do something with fields }; } // works @View('active', ['street1', 'street2']) class Address { street1: string; street2: string; } // broken @View('active', ['street1', 'street2']) class AddressBroken { street1: string; street2?: string; } ``` **Expected behavior:** Both scenarios should work above. **Actual behavior:** It appears that optional fields are causing the decorator to create invalid types. ``` Argument of type 'typeof AddressBroken' is not assignable to parameter of type 'new (...args: any[]) => { street1: any; street2: any; }'. Type 'AddressBroken' is not assignable to type '{ street1: any; street2: any; }'. Property 'street2' is optional in type 'AddressBroken' but required in type '{ street1: any; street2: any; }'. 1234 ``` **Playground Link:** [Playground Sample](http://www.typescriptlang.org/play/#src=%0D%0Afunction%20View%3CT%3E(name%3A%20string%2C%20fields%3A%20(keyof%20T)%5B%5D)%20%7B%0D%0A%20%20return%20(target%3A%20new(...args%3A%20any%5B%5D)%20%3D%3E%20T)%20%3D%3E%20%7B%0D%0A%20%20%20%20%2F%2F%20Do%20something%20with%20fields%0D%0A%20%20%7D%3B%0D%0A%7D%0D%0A%0D%0A%2F%2F%20works%0D%0A%40View('active'%2C%20%5B'street1'%2C%20'street2'%5D)%0D%0Aclass%20Address%20%7B%0D%0A%20%20street1%3A%20string%3B%0D%0A%20%20street2%3A%20string%3B%0D%0A%7D%0D%0A%0D%0A%2F%2F%20broken%0D%0A%40View('active'%2C%20%5B'street1'%2C%20'street2'%5D)%0D%0Aclass%20AddressBroken%20%7B%0D%0A%20%20street1%3A%20string%3B%0D%0A%20%20street2%3F%3A%20string%3B%0D%0A%7D%0D%0A)