Property '[Symbol.iterator]' is missing in type 'PartialTuple<ConstructorParams<T>>

TypeScript Version: 3.1 -> 3.7

Search Terms:
tuple, mapped tuple

Code

type Constructor = new (...args: any[]) => any;
type ConstructorParams<T extends Constructor> = T extends new (...args: infer P) => any ? P : never;
type PartialTuple<T extends any[]> = {[I in keyof T]: T[I] | undefined}
type ConstructorReturnType<T extends Constructor> =
    T extends new (...args: any[]) => infer R ? R : never;

function getClassFactory<T extends Constructor>(type: T) {
    type OptionalParams = PartialTuple<ConstructorParams<T>>;
    return getFunctionWithOptionalTypes<OptionalParams, ConstructorReturnType<T>>();
}

Expected behavior:
should compile correctly

Actual behavior:
shows error:

Type 'PartialTuple<ConstructorParams>' does not satisfy the constraint 'any[]'.
Property '[Symbol.iterator]' is missing in type 'PartialTuple<ConstructorParams>'.

Playground Link:
playground

I have to use 2 functions as I get A rest parameter must be of an array type. if I try to do it one function:

function getClassFactory<T extends Constructor>(type: T): new (...args: PartialTuple<ConstructorParams<T>>) => ConstructorReturnType<T> {
    return {} as any;
}

playground

I am trying to create a type that returns a function with parameters equal to that of a class constructor but where each parameter is T[P] | undefined.
I've done similar to this before

Start by reproducing the error in the two linked TypeScript Playgrounds across the stated TypeScript versions, focusing on the mapped tuple and constructor-parameter examples. Trace the compiler's handling of the PartialTuple constraint and rest-parameter validation. Done means both examples compile without the reported '[Symbol.iterator]' or array-type errors.