system/Session/Session.php
public function push(string $key, array $data)
	{
		if ($this->has($key) && is_array($value = $this->get($key)))
			   {
			$this->set($key, array_merge($value, $data));
		}
	}
public function push(string $key, array $data)
	{
		if ($this->has($key) && is_array($value = $this->get($key)))
			   {
			$this->set($key, array_merge($value, $data));
		}
	}
Push new value onto session value that is array.

@param string $key  Identifier of the session property we are interested in.
@param array  $data value to be pushed to existing session key.

@return void