Fix possibly undefined variables

src/Model/Event.php

@@ -644,15 +644,17 @@ class Event extends BaseObject
 	 */
 	private static function formatListForExport(array $events, $format)
 	{
+		$o = '';
+
 		if (!count($events)) {
-			return '';
+			return $o;
 		}
 
 		switch ($format) {
 			// Format the exported data as a CSV file.
 			case "csv":
 				header("Content-type: text/csv");
-				$o = '"Subject", "Start Date", "Start Time", "Description", "End Date", "End Time", "Location"' . PHP_EOL;
+				$o .= '"Subject", "Start Date", "Start Time", "Description", "End Date", "End Time", "Location"' . PHP_EOL;
 
 				foreach ($events as $event) {
 					/// @todo The time / date entries don't include any information about the

src/Model/Term.php

@@ -274,6 +274,7 @@ class Term
 				'network' => $item['author-network'], 'url' => $item['author-link']];
 			$tag['url'] = Contact::magicLinkByContact($author, $tag['url']);
 
+			$prefix = '';
 			if ($tag['type'] == TERM_HASHTAG) {
 				if ($orig_tag != $tag['url']) {
 					$item['body'] = str_replace($orig_tag, $tag['url'], $item['body']);