CodeIgniter 3 HMVC error running on PHP 7

When deploying a CodeIgniter 3 HMVC application to a server with PHP running, you will encounter an error about string.

A PHP Error was encountered
Severity: 8192

Message: strpos(): Non-string needles will be interpreted as strings in the future. Use an explicit chr() call to preserve the current behavior

Filename: MX/Router.php

You can fix this by modifying the file mentioned in the error message, MX/Router.php. The full file path is application\third_party\MX\Router.php.

This is the original code of set_class method:

public function set_class($class)
	{
		$suffix = $this->config->item('controller_suffix');
		if (strpos($class, $suffix) === FALSE)
		{
			$class .= $suffix;
		}
		parent::set_class($class);
	}

Replace it with

public function set_class($class)
	{
		/* $suffix = $this->config->item('controller_suffix');
		if (strpos($class, $suffix) === FALSE)
		{
			$class .= $suffix;
		} */
		$suffix = (string) $this->config->item('controller_suffix');
        if ($suffix && strpos($class, $suffix) === FALSE) {
            $class .= $suffix;
        }

		parent::set_class($class);
	}