Function add

add<E>(array?, element?): E[] | undefined | null
Returns the array that adds the given element
Type Parameters
- E
Parameters
- Optionalarray: null | E[]
  the arrays to inspect
- Optionalelement: null | E
  the element to add
Returns E[] | undefined | null
the array that adds the given element
Example
```
add(undefined, 'bar');    // ['bar']
add(['foo', 'bar'], undefined);    // ['foo', 'bar']
add(['foo', 'bar'], 'world');    // ['foo', 'bar', 'world']
```