src: Fix some more issues noticed by Psalm

src/controllers/About.php

@@ -61,6 +61,6 @@ public function about(Base $f3) {
             ],
         ];
 
-        echo $this->view->jsonSuccess($configuration);
+        $this->view->jsonSuccess($configuration);
     }
 }

src/controllers/Opml/Import.php

@@ -47,6 +47,8 @@ public function __construct(Authentication $authentication, Logger $logger, \dao
      * html
      *
      * @note Borrows from controllers/Sources.php:write
+     *
+     * @return void
      */
     public function add() {
         $this->authentication->needsLoggedIn();
@@ -78,8 +80,8 @@ public function add() {
             // show errors
             if (count($errors) > 0) {
                 http_response_code(202);
-                $messages = 'The following feeds could not be imported:';
-                $messages += $errors;
+                $messages[] = 'The following feeds could not be imported:';
+                $messages = array_merge($messages, $errors);
             } else { // On success bring them back to their subscription list
                 http_response_code(200);
                 $amount = count($this->imported);
@@ -149,7 +151,7 @@ private function processGroup(SimpleXMLElement $xml, array $tags = []) {
      * @param SimpleXMLElement $xml xml feed entry for item
      * @param array $tags of the entry
      *
-     * @return bool|string true on success or item title on error
+     * @return true|string true on success or item title on error
      */
     private function addSubscription(SimpleXMLElement $xml, array $tags) {
         // OPML Required attributes: text, xmlUrl, type

src/controllers/Opml/ImportPage.php

@@ -20,6 +20,8 @@ public function __construct(Authentication $authentication) {
     /**
      * Shows a simple html form
      * html
+     *
+     * @return void
      */
     public function show() {
         $this->authentication->needsLoggedIn();