WithFallback
Use TValue if truthy, otherwise use TFallback.
Example
type Example1 = WithFallback<null, 'fallback'> // 'fallback'
type Example2 = WithFallback<{}, 'fallback'> // 'fallback'
type Example3 = WithFallback<'value', 'fallback'> // 'value'
type Example4 = WithFallback<{ key: 'val' }, 'fallback'> // { key: 'val' }