diff --git a/classes/feedparser.php b/classes/feedparser.php
index fc2489e2d..4b9c63f56 100644
--- a/classes/feedparser.php
+++ b/classes/feedparser.php
@@ -43,10 +43,8 @@ class FeedParser {
 			foreach (libxml_get_errors() as $error) {
 				if ($error->level == LIBXML_ERR_FATAL) {
 					// currently only the first error is reported
-					if (!isset($this->error)) {
-						$this->error = $this->format_error($error);
-					}
-					$this->libxml_errors[] = $this->format_error($error);
+					$this->error ??= Errors::format_libxml_error($error);
+					$this->libxml_errors[] = Errors::format_libxml_error($error);
 				}
 			}
 		}
@@ -87,9 +85,7 @@ class FeedParser {
 					$this->type = $this::FEED_ATOM;
 					break;
 				default:
-					if (!isset($this->error)) {
-						$this->error = "Unknown/unsupported feed type";
-					}
+					$this->error ??= "Unknown/unsupported feed type";
 					return;
 				}
 			}
@@ -186,9 +182,7 @@ class FeedParser {
 			if ($this->link) $this->link = trim($this->link);
 
 		} else {
-			if (!isset($this->error)) {
-				$this->error = "Unknown/unsupported feed type";
-			}
+			$this->error ??= "Unknown/unsupported feed type";
 			return;
 		}
 	}
diff --git a/classes/handler/public.php b/classes/handler/public.php
index e1486e753..8ddf9bd3d 100755
--- a/classes/handler/public.php
+++ b/classes/handler/public.php
@@ -412,8 +412,7 @@ class Handler_Public extends Handler {
 				if (session_status() != PHP_SESSION_ACTIVE)
 					session_start();
 
-				if (!isset($_SESSION["login_error_msg"]))
-					$_SESSION["login_error_msg"] = __("Incorrect username or password");
+				$_SESSION["login_error_msg"] ??= __("Incorrect username or password");
 			}
 
 			$return = clean($_REQUEST['return']);
diff --git a/classes/pluginhost.php b/classes/pluginhost.php
index acc784902..4b85bc216 100755
--- a/classes/pluginhost.php
+++ b/classes/pluginhost.php
@@ -535,10 +535,7 @@ class PluginHost {
 		$method = strtolower($method);
 
 		if ($this->is_system($sender)) {
-			if (!isset($this->handlers[$handler])) {
-				$this->handlers[$handler] = [];
-			}
-
+			$this->handlers[$handler] ??= [];
 			$this->handlers[$handler][$method] = $sender;
 		}
 	}
@@ -641,8 +638,7 @@ class PluginHost {
 				owner_uid= ? AND name = ?");
 			$sth->execute([$this->owner_uid, $plugin]);
 
-			if (!isset($this->storage[$plugin]))
-				$this->storage[$plugin] = [];
+			$this->storage[$plugin] ??= [];
 
 			$content = serialize($this->storage[$plugin]);
 
@@ -673,14 +669,8 @@ class PluginHost {
 		if ($profile_id) {
 			$idx = get_class($sender);
 
-			if (!isset($this->storage[$idx])) {
-				$this->storage[$idx] = [];
-			}
-
-			if (!isset($this->storage[$idx][$profile_id])) {
-				$this->storage[$idx][$profile_id] = [];
-			}
-
+			$this->storage[$idx] ??= [];
+			$this->storage[$idx][$profile_id] ??= [];
 			$this->storage[$idx][$profile_id][$name] = $value;
 
 			$this->save_data(get_class($sender));
@@ -695,9 +685,7 @@ class PluginHost {
 	function set(Plugin $sender, string $name, $value): void {
 		$idx = get_class($sender);
 
-		if (!isset($this->storage[$idx]))
-			$this->storage[$idx] = [];
-
+		$this->storage[$idx] ??= [];
 		$this->storage[$idx][$name] = $value;
 
 		$this->save_data(get_class($sender));
@@ -709,8 +697,7 @@ class PluginHost {
 	function set_array(Plugin $sender, array $params): void {
 		$idx = get_class($sender);
 
-		if (!isset($this->storage[$idx]))
-			$this->storage[$idx] = [];
+		$this->storage[$idx] ??= [];
 
 		foreach ($params as $name => $value)
 			$this->storage[$idx][$name] = $value;
@@ -848,11 +835,13 @@ class PluginHost {
 	function add_filter_action(Plugin $sender, string $action_name, string $action_desc): void {
 		$sender_class = get_class($sender);
 
-		if (!isset($this->plugin_actions[$sender_class]))
-			$this->plugin_actions[$sender_class] = [];
+		$this->plugin_actions[$sender_class] ??= [];
 
-		array_push($this->plugin_actions[$sender_class],
-			array("action" => $action_name, "description" => $action_desc, "sender" => $sender));
+		$this->plugin_actions[$sender_class][] = [
+			"action" => $action_name,
+			"description" => $action_desc,
+			"sender" => $sender,
+		];
 	}
 
 	/**
diff --git a/classes/pref/prefs.php b/classes/pref/prefs.php
index ce9030cdc..3285ce200 100644
--- a/classes/pref/prefs.php
+++ b/classes/pref/prefs.php
@@ -185,7 +185,7 @@ class Pref_Prefs extends Handler_Protected {
 		$boolean_prefs = explode(",", clean($_POST["boolean_prefs"]));
 
 		foreach ($boolean_prefs as $pref) {
-			if (!isset($_POST[$pref])) $_POST[$pref] = 'false';
+			$_POST[$pref] ??= 'false';
 		}
 
 		$need_reload = false;
diff --git a/classes/rpc.php b/classes/rpc.php
index bb14225be..ef2cdfc49 100755
--- a/classes/rpc.php
+++ b/classes/rpc.php
@@ -753,12 +753,11 @@ class RPC extends Handler_Protected {
 	function hotkeyHelp(): void {
 		$info = self::get_hotkeys_info();
 		$imap = self::get_hotkeys_map();
-		$omap = array();
+		$omap = [];
 
 		foreach ($imap[1] as $sequence => $action) {
-			if (!isset($omap[$action])) $omap[$action] = array();
-
-			array_push($omap[$action], $sequence);
+			$omap[$action] ??= [];
+			$omap[$action][] = $sequence;
 		}
 
 		?>
diff --git a/include/functions.php b/include/functions.php
index 82e08ddb3..a7b15c165 100644
--- a/include/functions.php
+++ b/include/functions.php
@@ -108,8 +108,7 @@
 				$valid_langs[$lang] = $t;
 
 				$lang = substr($lang, 0, 2);
-				if (!isset($valid_langs[$lang]))
-					$valid_langs[$lang] = $t;
+				$valid_langs[$lang] ??= $t;
 			}
 
 			// break up string into pieces (languages and q factors)