diff --git a/diaspora/Diaspora_Connection.php b/diaspora/Diaspora_Connection.php
index d8390d70..05c21eb0 100644
--- a/diaspora/Diaspora_Connection.php
+++ b/diaspora/Diaspora_Connection.php
@@ -33,7 +33,6 @@ class Diaspora_Connection {
 		}
 
 		$this->cookiejar = tempnam(System::getTempPath(), 'cookies');
-		return $this;
 	}
 
 	public function __destruct() {
diff --git a/js_upload/js_upload.php b/js_upload/js_upload.php
index c0a2467d..4bf91de1 100644
--- a/js_upload/js_upload.php
+++ b/js_upload/js_upload.php
@@ -188,7 +188,7 @@ class js_upload_qqFileUploader
 	private $sizeLimit;
 
 	/**
-	 * @var js_upload_qqUploadedFileXhr|js_upload_qqUploadedFileForm
+	 * @var js_upload_qqUploadedFileXhr|js_upload_qqUploadedFileForm|false
 	 */
 	private $file;
 
diff --git a/libravatar/Services/Libravatar.php b/libravatar/Services/Libravatar.php
index e51ef070..8b3dd493 100644
--- a/libravatar/Services/Libravatar.php
+++ b/libravatar/Services/Libravatar.php
@@ -361,7 +361,7 @@ class Services_Libravatar
     protected function domainGet($identifier)
     {
         if ($identifier === null) {
-            return null;
+            return '';
         }
 
         // What are we, email or openid? Split ourself up and get the
diff --git a/mailstream/mailstream.php b/mailstream/mailstream.php
index 5228b168..98654831 100644
--- a/mailstream/mailstream.php
+++ b/mailstream/mailstream.php
@@ -179,7 +179,7 @@ function mailstream_post_hook(array &$item)
 function mailstream_do_images(array &$item, array &$attachments)
 {
 	if (!DI::pConfig()->get($item['uid'], 'mailstream', 'attachimg')) {
-		return;
+		return $attachments;
 	}
 
 	$attachments = [];
diff --git a/membersince/membersince.php b/membersince/membersince.php
index 448b8cf2..df6388c6 100644
--- a/membersince/membersince.php
+++ b/membersince/membersince.php
@@ -17,7 +17,11 @@ function membersince_install()
 	Hook::register('profile_advanced', 'addon/membersince/membersince.php', 'membersince_display');
 }
 
-function membersince_display(array &$b)
+/**
+ * @param array|string|null $b
+ * @return void
+ */
+function membersince_display(&$b)
 {
 	$uid = DI::userSession()->getLocalUserId();
 
@@ -59,7 +63,7 @@ function membersince_display(array &$b)
 		$div->appendChild($entry);
 		$elm->parentNode->insertBefore($div, $elm->nextSibling);
 
-		$b = $doc->saveHTML();
+		$b = (string) $doc->saveHTML();
 	} else {
 		// Works in Vier.
 		$b = preg_replace('/<\/dl>/', "</dl>\n\n\n<dl id=\"aprofile-membersince\" class=\"aprofile\">\n<dt>" . DI::l10n()->t('Member since:') . "</dt>\n<dd>" . DateTimeFormat::local($user['register_date']) . "</dd>\n</dl>", $b, 1);
diff --git a/notifyall/notifyall.php b/notifyall/notifyall.php
index d37bac56..f814c4f5 100644
--- a/notifyall/notifyall.php
+++ b/notifyall/notifyall.php
@@ -57,7 +57,7 @@ function notifyall_post()
 
 	$notifyEmail = new NotifyAllEmail(DI::l10n(), DI::config(), DI::baseUrl(), $text);
 
-	foreach ($recipients as $recipient) {
+	foreach (DBA::toArray($recipients) as $recipient) {
 		DI::emailer()->send($notifyEmail->withRecipient($recipient['email']));
 	}
 
diff --git a/phpmailer/phpmailer.php b/phpmailer/phpmailer.php
index f4bb7753..10287a04 100644
--- a/phpmailer/phpmailer.php
+++ b/phpmailer/phpmailer.php
@@ -28,10 +28,14 @@ function phpmailer_load_config(ConfigFileManager $loader)
 }
 
 /**
- * @param IEmail $email
+ * @param null|IEmail $email
  */
-function phpmailer_emailer_send_prepare(IEmail &$email)
+function phpmailer_emailer_send_prepare(?IEmail &$email)
 {
+	if ($email === null) {
+		return;
+	}
+
 	// Passing `true` enables exceptions
 	$mailer = new PHPMailer(true);
 	try {
diff --git a/pnut/lib/phpnut.php b/pnut/lib/phpnut.php
index ff765243..716945ed 100644
--- a/pnut/lib/phpnut.php
+++ b/pnut/lib/phpnut.php
@@ -1025,7 +1025,7 @@ class phpnut
      * see: https://docs.pnut.io/resources/posts/search
      * @param string $query The search query. Supports
      * normal search terms. Searches post text.
-     * @return array An array of associative arrays, each representing one post.
+     * @return string|array|false An array of associative arrays, each representing one post.
      * or false on error
      */
     public function searchPosts(array $params=[], string $query='', string $order='default')
@@ -1769,7 +1769,7 @@ class phpnut
      * see: https://docs.pnut.io/resources/messages/search
      * @param string $query The search query. Supports
      * normal search terms. Searches common channel raw.
-     * @return array An array of associative arrays, each representing one channel.
+     * @return string|array|false An array of associative arrays, each representing one channel.
      * or false on error
      */
     public function searchMessages(array $params=[], string $query='', string $order='default')
diff --git a/statusnet/library/codebirdsn.php b/statusnet/library/codebirdsn.php
index 9807d97f..bffca163 100644
--- a/statusnet/library/codebirdsn.php
+++ b/statusnet/library/codebirdsn.php
@@ -976,7 +976,7 @@ class CodebirdSN
      * @param string $method The method that has been called
      * @param string $reply  The actual reply, JSON-encoded or URL-encoded
      *
-     * @return array|object The parsed reply
+     * @return string|array|object The parsed reply
      */
     protected function _parseApiReply($method, $reply)
     {
diff --git a/statusnet/library/statusnetoauth.php b/statusnet/library/statusnetoauth.php
index c32b2b4f..da21be58 100644
--- a/statusnet/library/statusnetoauth.php
+++ b/statusnet/library/statusnetoauth.php
@@ -12,7 +12,7 @@ require_once __DIR__ . DIRECTORY_SEPARATOR . 'twitteroauth.php';
  */
 class StatusNetOAuth extends TwitterOAuth
 {
-	function get_maxlength()
+	public function get_maxlength()
 	{
 		$config = $this->get($this->host . 'statusnet/config.json');
 		if (empty($config)) {
@@ -21,27 +21,27 @@ class StatusNetOAuth extends TwitterOAuth
 		return $config->site->textlimit;
 	}
 
-	function accessTokenURL()
+	public function accessTokenURL()
 	{
 		return $this->host . 'oauth/access_token';
 	}
 
-	function authenticateURL()
+	public function authenticateURL()
 	{
 		return $this->host . 'oauth/authenticate';
 	}
 
-	function authorizeURL()
+	public function authorizeURL()
 	{
 		return $this->host . 'oauth/authorize';
 	}
 
-	function requestTokenURL()
+	public function requestTokenURL()
 	{
 		return $this->host . 'oauth/request_token';
 	}
 
-	function __construct($apipath, $consumer_key, $consumer_secret, $oauth_token = NULL, $oauth_token_secret = NULL)
+	public function __construct($apipath, $consumer_key, $consumer_secret, $oauth_token = NULL, $oauth_token_secret = NULL)
 	{
 		parent::__construct($consumer_key, $consumer_secret, $oauth_token, $oauth_token_secret);
 		$this->host = $apipath;
@@ -52,9 +52,9 @@ class StatusNetOAuth extends TwitterOAuth
 	 *
 	 * Copied here from the TwitterOAuth library and complemented by applying the proxy settings of Friendica
 	 *
-	 * @return array|object API results
+	 * @return array|object|mixed API results
 	 */
-	function http($url, $method, $postfields = NULL)
+	public function http($url, $method, $postfields = NULL)
 	{
 		$this->http_info = [];
 		$ci = curl_init();
diff --git a/statusnet/library/twitteroauth.php b/statusnet/library/twitteroauth.php
index bf413d23..bab66195 100644
--- a/statusnet/library/twitteroauth.php
+++ b/statusnet/library/twitteroauth.php
@@ -45,11 +45,11 @@ class TwitterOAuth
 	public $http_header;
 	/**
 	 * Contains the last HTTP request info
-	 * @var string
+	 * @var array
 	 */
 	public $http_info;
 
-	/** @var OAuthToken */
+	/** @var OAuthToken|null */
 	private $token;
 	/** @var OAuthConsumer */
 	private $consumer;
@@ -59,27 +59,27 @@ class TwitterOAuth
 	/**
 	 * Set API URLS
 	 */
-	function accessTokenURL()
+	public function accessTokenURL()
 	{
 		return 'https://api.twitter.com/oauth/access_token';
 	}
 
-	function authenticateURL()
+	public function authenticateURL()
 	{
 		return 'https://twitter.com/oauth/authenticate';
 	}
 
-	function authorizeURL()
+	public function authorizeURL()
 	{
 		return 'https://twitter.com/oauth/authorize';
 	}
 
-	function requestTokenURL()
+	public function requestTokenURL()
 	{
 		return 'https://api.twitter.com/oauth/request_token';
 	}
 
-	function __construct($consumer_key, $consumer_secret, $oauth_token = null, $oauth_token_secret = null)
+	public function __construct($consumer_key, $consumer_secret, $oauth_token = null, $oauth_token_secret = null)
 	{
 		$this->sha1_method = new OAuthSignatureMethod_HMAC_SHA1();
 		$this->consumer = new OAuthConsumer($consumer_key, $consumer_secret);
@@ -96,7 +96,7 @@ class TwitterOAuth
 	 * @param callable $oauth_callback
 	 * @return array
 	 */
-	function getRequestToken($oauth_callback = null)
+	public function getRequestToken($oauth_callback = null)
 	{
 		$parameters = [];
 		if (!empty($oauth_callback)) {
@@ -114,7 +114,7 @@ class TwitterOAuth
 	 *
 	 * @return string
 	 */
-	function getAuthorizeURL($token, $sign_in_with_twitter = TRUE)
+	public function getAuthorizeURL($token, $sign_in_with_twitter = TRUE)
 	{
 		if (is_array($token)) {
 			$token = $token['oauth_token'];
@@ -137,7 +137,7 @@ class TwitterOAuth
 	 *                "user_id" => "9436992",
 	 *                "screen_name" => "abraham")
 	 */
-	function getAccessToken($oauth_verifier = FALSE)
+	public function getAccessToken($oauth_verifier = FALSE)
 	{
 		$parameters = [];
 		if (!empty($oauth_verifier)) {
@@ -162,7 +162,7 @@ class TwitterOAuth
 	 *                "screen_name" => "abraham",
 	 *                "x_auth_expires" => "0")
 	 */
-	function getXAuthToken($username, $password)
+	public function getXAuthToken($username, $password)
 	{
 		$parameters = [];
 		$parameters['x_auth_username'] = $username;
@@ -182,7 +182,7 @@ class TwitterOAuth
 	 * @param array $parameters
 	 * @return mixed|string
 	 */
-	function get($url, $parameters = [])
+	public function get($url, $parameters = [])
 	{
 		$response = $this->oAuthRequest($url, 'GET', $parameters);
 		if ($this->format === 'json' && $this->decode_json) {
@@ -199,7 +199,7 @@ class TwitterOAuth
 	 * @param array $parameters
 	 * @return mixed|string
 	 */
-	function post($url, $parameters = [])
+	public function post($url, $parameters = [])
 	{
 		$response = $this->oAuthRequest($url, 'POST', $parameters);
 		if ($this->format === 'json' && $this->decode_json) {
@@ -216,7 +216,7 @@ class TwitterOAuth
 	 * @param array $parameters
 	 * @return mixed|string
 	 */
-	function delete($url, $parameters = [])
+	public function delete($url, $parameters = [])
 	{
 		$response = $this->oAuthRequest($url, 'DELETE', $parameters);
 		if ($this->format === 'json' && $this->decode_json) {
@@ -234,7 +234,7 @@ class TwitterOAuth
 	 * @param array $parameters
 	 * @return mixed|string
 	 */
-	function oAuthRequest($url, $method, $parameters)
+	public function oAuthRequest($url, $method, $parameters)
 	{
 		if (strrpos($url, 'https://') !== 0 && strrpos($url, 'http://') !== 0) {
 			$url = "{$this->host}{$url}.{$this->format}";
@@ -258,9 +258,9 @@ class TwitterOAuth
 	 * @param string $url
 	 * @param string $method
 	 * @param mixed  $postfields
-	 * @return string API results
+	 * @return string|bool|mixed API results
 	 */
-	function http($url, $method, $postfields = null)
+	public function http($url, $method, $postfields = null)
 	{
 		$this->http_info = [];
 		$ci = curl_init();
@@ -305,7 +305,7 @@ class TwitterOAuth
 	 * @param string $header
 	 * @return int
 	 */
-	function getHeader($ch, $header)
+	public function getHeader($ch, $header)
 	{
 		$i = strpos($header, ':');
 		if (!empty($i)) {
diff --git a/tumblr/tumblr.php b/tumblr/tumblr.php
index 4415e2de..9e691bf2 100644
--- a/tumblr/tumblr.php
+++ b/tumblr/tumblr.php
@@ -791,7 +791,7 @@ function tumblr_fetch_dashboard(int $uid, int $last_poll)
 	$dashboard = tumblr_get($uid, 'user/dashboard', $parameters);
 	if ($dashboard->meta->status > 399) {
 		DI::logger()->notice('Error fetching dashboard', ['meta' => $dashboard->meta, 'response' => $dashboard->response, 'errors' => $dashboard->errors]);
-		return [];
+		return;
 	}
 
 	if (empty($dashboard->response->posts)) {
diff --git a/webdav_storage/src/WebDavConfig.php b/webdav_storage/src/WebDavConfig.php
index 2236e97a..320b06a2 100644
--- a/webdav_storage/src/WebDavConfig.php
+++ b/webdav_storage/src/WebDavConfig.php
@@ -52,7 +52,7 @@ class WebDavConfig implements ICanConfigureStorage
 		$this->config = $config;
 		$this->client = $client;
 
-		$this->authOptions = null;
+		$this->authOptions = [];
 
 		if (!empty($this->config->get('webdav', 'username'))) {
 			$this->authOptions = [