Order matters while Resolving a Union Type and its conditional keys

[azizhk]

TypeScript Version: 3.4.0-dev.20190202

Search Terms: Conditional Resolution, Optionals

Code

interface RangeProps {
    range?: false;
    onApply?: (value: Date) => void;
}
interface SingleProps {
    range: true;
    onApply?: (value: [Date, Date]) => void;
}
type CalendarProps = RangeProps | SingleProps;

function apply (props: CalendarProps) {
    if (props.onApply) {
        if (props.range) {
            // Should work as already inside props.onApply check.
            props.onApply([new Date(), new Date()]);
        } else {
            // Should work as already inside props.onApply check.
            props.onApply(new Date());
        }
    }
}

Expected behavior:
Above code should not throw error.

Actual behavior:
Error at lines after comment: Cannot invoke an object which is possibly 'undefined'.

Playground Link:

Related Issues:
Tried my best, sorry but could not find any
Please also change/suggest the title of issue if it does not reflect on the error.

[RyanCavanaugh]

Basically a duplicate of #28131

[azizhk]

Closing then in favor of #28131