diff --git a/wwwroot/inc/caching.php b/wwwroot/inc/caching.php
index 4bd4fd7d2..cad455380 100644
--- a/wwwroot/inc/caching.php
+++ b/wwwroot/inc/caching.php
@@ -67,7 +67,7 @@ function HTTPDateToUnixTime ($string)
 	$formats['asctime'] = '/^(Sun|Mon|Tue|Wed|Thu|Fri|Sat) (Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec) (\d{2}| \d{1}) (\d{2}):(\d{2}):(\d{2}) (\d{4})$/';
 
 	$matches = array();
-	if (preg_match ($formats['rfc1123'], $string, $matches))
+	if (preg_match ($formats['rfc1123'], $string ?? "", $matches))
 	{
 		$hours = $matches[5];
 		$minutes = $matches[6];
@@ -76,7 +76,7 @@ function HTTPDateToUnixTime ($string)
 		$day = $matches[2];
 		$year = $matches[4];
 	}
-	elseif (preg_match ($formats['rfc850'], $string, $matches))
+	elseif (preg_match ($formats['rfc850'], $string ?? "", $matches))
 	{
 		$hours = $matches[5];
 		$minutes = $matches[6];
@@ -85,7 +85,7 @@ function HTTPDateToUnixTime ($string)
 		$day = $matches[2];
 		$year = $matches[4];
 	}
-	elseif (preg_match ($formats['asctime'], $string, $matches))
+	elseif (preg_match ($formats['asctime'], $string ?? "", $matches))
 	{
 		$hours = $matches[4];
 		$minutes = $matches[5];
diff --git a/wwwroot/inc/functions.php b/wwwroot/inc/functions.php
index 5a6fbdc9f..c75c1b2c3 100644
--- a/wwwroot/inc/functions.php
+++ b/wwwroot/inc/functions.php
@@ -1216,7 +1216,7 @@ function findAllEndpoints ($object_id, $fallback = '')
 // $record['href'] is set to URL if it is specified in the input value
 function parseWikiLink (&$record)
 {
-	if (! preg_match ('/^\[\[(.+)\]\]$/', $record['value'], $matches))
+	if (! preg_match ('/^\[\[(.+)\]\]$/', $record['value'] ?? "", $matches))
 		$record['o_value'] = $record['value'];
 	else
 	{
@@ -1233,7 +1233,7 @@ function execGMarker ($line)
 {
 	return preg_replace ('/^.+%GSKIP%/', '',
 		preg_replace ('/^(.+)%GPASS%/', '\\1 ',
-			preg_replace ('/%L\d+,\d+(H|V|)%/', '', $line)));
+			preg_replace ('/%L\d+,\d+(H|V|)%/', '', $line ?? "")));
 }
 
 // extract the layout information from the %L...% marker in the dictionary info
@@ -1402,7 +1402,7 @@ function parseAutoPortsConfig ($schema)
 {
 	$ret = array();
 
-	foreach (explode ('+', $schema) as $product)
+	foreach (explode ('+', $schema ?? "") as $product)
 	{
 		$tmp = explode ('*', $product);
 		if (count ($tmp) > 4 || count ($tmp) < 3)
diff --git a/wwwroot/inc/interface-lib.php b/wwwroot/inc/interface-lib.php
index a8d7b34f8..927379d38 100644
--- a/wwwroot/inc/interface-lib.php
+++ b/wwwroot/inc/interface-lib.php
@@ -1210,14 +1210,14 @@ function stringForTD ($string, $maxlen = 30)
 function stringForTextInputValue ($string, $maxlen = 30)
 {
 	if ($maxlen != 0)
-		$string = mb_substr ($string, 0, $maxlen);
+		$string = mb_substr ($string ?? "", 0, $maxlen);
 	return htmlspecialchars ($string, ENT_QUOTES, 'UTF-8');
 }
 
 // "<TEXTAREA>%s</TEXTAREA>"
 function stringForTextarea ($string)
 {
-	return htmlspecialchars ($string, ENT_QUOTES, 'UTF-8');
+	return htmlspecialchars ($string ?? "", ENT_QUOTES, 'UTF-8');
 }
 
 // <OPTION>%s</OPTION>
diff --git a/wwwroot/inc/popup.php b/wwwroot/inc/popup.php
index dfc2f717c..d6d0f484c 100644
--- a/wwwroot/inc/popup.php
+++ b/wwwroot/inc/popup.php
@@ -137,7 +137,7 @@ function findSparePorts ($port_info, $filter)
 				}
 			$rows_by_pn = array();
 		}
-		$prev_object_id = $row['object_id'];
+		$prev_object_id = $row['object_id'] ?? "";
 		if ($row)
 			$rows_by_pn[$row['name']][] = $row;
 		else
diff --git a/wwwroot/inc/solutions.php b/wwwroot/inc/solutions.php
index 1f8b1ea2a..4d6757764 100644
--- a/wwwroot/inc/solutions.php
+++ b/wwwroot/inc/solutions.php
@@ -472,7 +472,7 @@ function proxyStaticURI ($URI)
 	if
 	(
 		! preg_match (RE_STATIC_URI, $URI, $matches) ||
-		! array_key_exists (strtolower ($matches[1]), $content_type)
+		! array_key_exists (strtolower ($matches[1] ?? ""), $content_type)
 	)
 		printStatic404();
 	global $local_staticdir, $racktables_staticdir;