src/Arrays/Fluent.php
public function add($key, $value = null)
	{
		if (is_null($value))
		{
			$this->offsetSet(null, $key);
		}
		else
		{
			if (is_null($this->get($key)))
			{
				$this->set($key, $value);
			}
		}

		return $this;
	}
public function add($key, $value = null)
	{
		if (is_null($value))
		{
			$this->offsetSet(null, $key);
		}
		else
		{
			if (is_null($this->get($key)))
			{
				$this->set($key, $value);
			}
		}

		return $this;
	}
Method: add
=========================================================================
Add an item to the collection by key, if it doesn't exist.

For example:

```php
$data = Arr::a(['a' => ['b' => ['c' => 'd']]]);
$data->add('a', '123'); // fails
$data->add('z', '123'); // works
```

Parameters:
-------------------------------------------------------------------------
$key - Can be a single key, "dot" separated keys or an array of keys.
$value - The value to set on the collection.

Returns:
-------------------------------------------------------------------------
static