Function defaultIfEmpty`Const`

defaultIfEmpty<T>(): (src: Iterable) => Iterable
Returns an iterable that yields the source items or undefined when the source is empty.

Curried version of _defaultIfEmpty.
Type Parameters
- T
  Element type produced by the source iterable.
Returns (src: Iterable) => Iterable
A deferred iterable producing the original sequence or a single undefined when no elements exist.
Example
```
const values = [..._defaultIfEmpty([1, 2, 3])];
console.log(values); // [1, 2, 3]
```
or using the curried version:
```
const values = [...pipeInto([], defaultIfEmpty<number>())];
console.log(values); // [undefined]
```