Fix comments

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

lib/private/Mail/EMailTemplate.php

 	 * @param string $text Note: When $plainText falls back to this, HTML is automatically escaped in the HTML email
 	 * @param string $metaInfo Note: When $plainMetaInfo falls back to this, HTML is automatically escaped in the HTML email
 	 * @param string $icon Absolute path, must be 16*16 pixels
-	 * @param string $plainText Text that is used in the plain text email
+	 * @param string|bool $plainText Text that is used in the plain text email
 	 *   if empty the $text is used, if false none will be used
-	 * @param string $plainMetaInfo Meta info that is used in the plain text email
+	 * @param string|bool $plainMetaInfo Meta info that is used in the plain text email
 	 *   if empty the $metaInfo is used, if false none will be used
 	 * @since 12.0.0
 	 */
-	public function addBodyListItem(string $text, string $metaInfo = '', string $icon = '', string $plainText = '', string $plainMetaInfo = '') {
+	public function addBodyListItem(string $text, string $metaInfo = '', string $icon = '', $plainText = '', $plainMetaInfo = '') {
 		$this->ensureBodyListOpened();
 
 		if ($plainText === '') {

lib/private/Mail/Message.php

 	/**
 	 * Set the subject of this message.
 	 *
-	 * @param $subject
-	 * @return $this
+	 * @param string $subject
+	 * @return IMessage
 	 */
-	public function setSubject($subject): IMessage {
+	public function setSubject(string $subject): IMessage {
 		$this->swiftMessage->setSubject($subject);
 		return $this;
 	}

lib/public/Mail/IEMailTemplate.php

 	 * @param string $text; Note: When $plainText falls back to this, HTML is automatically escaped in the HTML email
 	 * @param string $metaInfo; Note: When $plainMetaInfo falls back to this, HTML is automatically escaped in the HTML email
 	 * @param string $icon Absolute path, must be 16*16 pixels
-	 * @param string $plainText Text that is used in the plain text email
+	 * @param string|bool $plainText Text that is used in the plain text email
 	 *   if empty the $text is used, if false none will be used
-	 * @param string $plainMetaInfo Meta info that is used in the plain text email
+	 * @param string|bool $plainMetaInfo Meta info that is used in the plain text email
 	 *   if empty the $metaInfo is used, if false none will be used
 	 * @since 12.0.0
 	 */
-	public function addBodyListItem(string $text, string $metaInfo = '', string $icon = '', string $plainText = '', string $plainMetaInfo = '');
+	public function addBodyListItem(string $text, string $metaInfo = '', string $icon = '', $plainText = '', $plainMetaInfo = '');
 
 	/**
 	 * Adds a button group of two buttons to the body of the email