Iridium Module - Blank Page - Debug Error

[katea]

This is the full code for that section:

		$confirmation['fields'][] = array(
				'title' => MODULE_PAYMENT_IRIDIUM_TEXT_CARD_NUMBER,
				'field' => substr($this->card_number, 0, 4) .
					str_repeat('X', (strlen($this->card_number) - 8)) .
					substr($this->card_number, -4)
			);