diff --git a/classes/feeditem/atom.php b/classes/feeditem/atom.php
index 36a2e91f5..cac6d8c54 100755
--- a/classes/feeditem/atom.php
+++ b/classes/feeditem/atom.php
@@ -70,7 +70,7 @@ class FeedItem_Atom extends FeedItem_Common {
 	 *
 	 * @return string the rewritten XML or original $content
 	 */
-	private function rewrite_content_to_base(?string $base = null, string $content) {
+	private function rewrite_content_to_base(?string $base = null, ?string $content = '') {
 
 		if (!empty($base) && !empty($content)) {
 
diff --git a/classes/feedparser.php b/classes/feedparser.php
index 3ed0647d2..fc2489e2d 100644
--- a/classes/feedparser.php
+++ b/classes/feedparser.php
@@ -200,7 +200,7 @@ class FeedParser {
 
 	// libxml may have invalid unicode data in error messages
 	function error() : string {
-		return UConverter::transcode($this->error, 'UTF-8', 'UTF-8');
+		return UConverter::transcode($this->error ?? '', 'UTF-8', 'UTF-8');
 	}
 
 	/** @return array<string> - WARNING: may return invalid unicode data */
diff --git a/classes/feeds.php b/classes/feeds.php
index 6f812b98c..a06486883 100755
--- a/classes/feeds.php
+++ b/classes/feeds.php
@@ -23,7 +23,7 @@ class Feeds extends Handler_Protected {
 	 */
 	private function _format_headlines_list($feed, string $method, string $view_mode, int $limit, bool $cat_view,
 					int $offset, string $override_order, bool $include_children, ?int $check_first_id = null,
-					bool $skip_first_id_check, string $order_by): array {
+					?bool $skip_first_id_check = false, ? string $order_by = ''): array {
 
 		$disable_cache = false;
 
diff --git a/classes/pref/system.php b/classes/pref/system.php
index 10f196b55..806291c72 100644
--- a/classes/pref/system.php
+++ b/classes/pref/system.php
@@ -138,7 +138,7 @@ class Pref_System extends Handler_Administrative {
 					$sth->execute($errno_values);
 
 					while ($line = $sth->fetch()) {
-						foreach ($line as $k => $v) { $line[$k] = htmlspecialchars($v); }
+						foreach ($line as $k => $v) { $line[$k] = htmlspecialchars($v ?? ''); }
 						?>
 						<tr>
 							<td class='errno'>
diff --git a/lib/jimIcon.php b/lib/jimIcon.php
index eaa768272..eb9a51458 100644
--- a/lib/jimIcon.php
+++ b/lib/jimIcon.php
@@ -31,7 +31,7 @@ class jimIcon {
                 }
                 if ($a != 127)
                         $this->all_transaprent = 0;
-                return imagecolorallocatealpha($img, $r, $g, $b, $a);
+                return imagecolorallocatealpha($img, $r, $g, $b, (int) $a);
         }
 
         // Given a string with the contents of an .ICO,