minor fixes.

framework/i18n/MessageSource.php

@@ -114,8 +114,10 @@ class MessageSource extends Component
 				'language' => $language,
 			]);
 			$this->trigger(self::EVENT_MISSING_TRANSLATION, $event);
-			if ($event->translatedMessage !== false) {
+			if ($event->translatedMessage !== null) {
 				return $this->_messages[$key][$message] = $event->translatedMessage;
+			} else {
+				return $this->_messages[$key][$message] = false;
 			}
 		}
 		return false;

framework/i18n/MissingTranslationEvent.php

@@ -23,11 +23,10 @@ class MissingTranslationEvent extends Event
 	 */
 	public $message;
 	/**
-	 * @var string|boolean the translated message. An event handler may overwrite this property
-	 * with a translated version of [[message]] if possible. Defaults to false meaning no translation
-	 * is available.
+	 * @var string the translated message. An event handler may overwrite this property
+	 * with a translated version of [[message]] if possible. If not set (null), it means the message is not translated.
 	 */
-	public $translatedMessage = false;
+	public $translatedMessage;
 	/**
 	 * @var string the category that the message belongs to
 	 */