remove hashtags filter stability improvement

src/client/filters/RemoveHashtags.js

@@ -1,5 +1,5 @@
 export default function(app) {
     app.filter('removeHashtags', () => {
-        return string => string.replace(/(#[^\s]+)/g, '');
+        return string => string ? string.replace(/(#[^\s]+)/g, '') : string;
     });
 };