Potential bug in Swift compiler?

BaseClass.swift

import Foundation

public class BaseClass<H> {
    public init?() {
        
    }
}

ClassA.swift

import Foundation

public class ClassA: BaseClass<Int> {
    // NOTE: Uncommenting this makes the error go away. Why???
    //public convenience init?(_ whatever: Int) { fatalError() }
}

ClassB.swift

import Foundation

public class ClassB: BaseClass<Bool> {
    public func makeA() -> ClassA? {
        return ClassA() // error: '() -> ClassA' is not convertible to '() -> ClassA?'
    }
}