Arr.php
public static function add(array& $array, string $key, $value, string $delimiter = null)
    {
        if (null === static::get($array, $key, null, $delimiter)) {
            static::set($array, $key, $value, $delimiter);
        }
    }
public static function add(array& $array, string $key, $value, string $delimiter = null)
    {
        if (null === static::get($array, $key, null, $delimiter)) {
            static::set($array, $key, $value, $delimiter);
        }
    }
public static function add ( array & $ array , string $ key , $ value , string $ delimiter = null ) { if ( null === static :: get ( $ array , $ key , null , $ delimiter ) ) { static :: set ( $ array , $ key , $ value , $ delimiter ) ; } }
Adds an element to the given array but only if it does not yet exist.

Note: Null as value of an item is considered a non-existing item for the purposes
of this method.

@param   array   $array      The array to which the element should be added.
@param   string  $key        The key at which the value should be added.
@param   mixed   $value      The value of the element.
@param   string  $delimiter  The delimiter to use when exploding the key into parts.
Adds an element to the given array but only if it does not yet exist .