diff --git a/src/Control/CwpBasicAuthMiddleware.php b/src/Control/CwpBasicAuthMiddleware.php
index 875101d..8cb1395 100644
--- a/src/Control/CwpBasicAuthMiddleware.php
+++ b/src/Control/CwpBasicAuthMiddleware.php
@@ -43,12 +43,12 @@ public function setWhitelistedIps($whitelistedIps)
             if (!$ipList) {
                 continue;
             }
-            $ips = array_map('trim', explode(',', $ipList));
+            $ips = array_map('trim', explode(',', $ipList ?? ''));
             $whitelistedIps = array_merge($whitelistedIps, $ips);
         }
 
         // Return unique values with keys reset
-        $this->whitelistedIps = array_values(array_unique($whitelistedIps));
+        $this->whitelistedIps = array_values(array_unique($whitelistedIps ?? []));
         return $this;
     }
 
@@ -80,7 +80,7 @@ protected function ipMatchesWhitelist()
         }
 
         $userIp = $_SERVER['REMOTE_ADDR'];
-        if (in_array($userIp, $whitelist)) {
+        if (in_array($userIp, $whitelist ?? [])) {
             return true;
         }
 
diff --git a/src/Control/InitialisationMiddleware.php b/src/Control/InitialisationMiddleware.php
index 1ad597a..309d40c 100644
--- a/src/Control/InitialisationMiddleware.php
+++ b/src/Control/InitialisationMiddleware.php
@@ -142,13 +142,13 @@ protected function configureProxyDomainExclusions()
 
         // Merge with exsiting if needed.
         if (Environment::getEnv('NO_PROXY')) {
-            $noProxy = array_merge(explode(',', Environment::getEnv('NO_PROXY')), $noProxy);
+            $noProxy = array_merge(explode(',', Environment::getEnv('NO_PROXY') ?? ''), $noProxy);
         }
 
         /*
          * Set the environment varial for NO_PROXY the same way the
          * proxy variables are set above
          */
-        putenv('NO_PROXY=' . implode(',', array_unique($noProxy)));
+        putenv('NO_PROXY=' . implode(',', array_unique($noProxy ?? [])));
     }
 }
diff --git a/src/Extension/CWPVersionExtension.php b/src/Extension/CWPVersionExtension.php
index 2825319..cebbfba 100644
--- a/src/Extension/CWPVersionExtension.php
+++ b/src/Extension/CWPVersionExtension.php
@@ -27,6 +27,6 @@ public function getCWPVersionNumber()
 
         // Example: "2.2.x-dev"
         $cwpCore = $modules['cwp/cwp-core'];
-        return (string) substr($cwpCore, 0, strpos($cwpCore, '.', 2));
+        return (string) substr($cwpCore ?? '', 0, strpos($cwpCore ?? '', '.', 2));
     }
 }
diff --git a/src/Extension/LoginAttemptNotifications.php b/src/Extension/LoginAttemptNotifications.php
index 0b8bc96..74c4937 100644
--- a/src/Extension/LoginAttemptNotifications.php
+++ b/src/Extension/LoginAttemptNotifications.php
@@ -51,7 +51,7 @@ public function init()
                 $lastVisitedObj->setValue($sessionLastVisited);
                 $elapsed = $lastVisitedObj->TimeDiff();
                 $failures = $meantimeLoginAttempts->filter(['Status' => 'Failure'])->count();
-                $IPs = array_unique($meantimeLoginAttempts->column('IP'));
+                $IPs = array_unique($meantimeLoginAttempts->column('IP') ?? []);
 
                 if ($attempts == 1) {
                     $statusString = $failures ? "a failed" : "a successful";
diff --git a/src/Extension/RichLinksExtension.php b/src/Extension/RichLinksExtension.php
index 92f9887..1d2b56f 100644
--- a/src/Extension/RichLinksExtension.php
+++ b/src/Extension/RichLinksExtension.php
@@ -36,18 +36,18 @@ public function RichLinks()
         $content = $this->owner->value;
 
         // Find all file links for processing.
-        preg_match_all('/<a.*href="\[file_link,id=([0-9]+)\].*".*>.*<\/a>/U', $content, $matches);
+        preg_match_all('/<a.*href="\[file_link,id=([0-9]+)\].*".*>.*<\/a>/U', $content ?? '', $matches);
 
         // Attach the file type and size to each of the links.
-        for ($i = 0; $i < count($matches[0]); $i++) {
+        for ($i = 0; $i < count($matches[0] ?? []); $i++) {
             $file = DataObject::get_by_id(File::class, $matches[1][$i]);
             if ($file) {
                 $size = $file->getSize();
-                $ext = strtoupper($file->getExtension());
+                $ext = strtoupper($file->getExtension() ?? '');
                 // Replace the closing </a> tag with the size span (and reattach the closing tag).
-                $newLink = substr($matches[0][$i], 0, strlen($matches[0][$i]) - 4)
+                $newLink = substr($matches[0][$i] ?? '', 0, strlen($matches[0][$i] ?? '') - 4)
                     . "<span class='fileExt'> [$ext, $size]</span></a>";
-                $content = str_replace($matches[0][$i], $newLink, $content);
+                $content = str_replace($matches[0][$i] ?? '', $newLink ?? '', $content ?? '');
             }
         }
 
@@ -57,7 +57,7 @@ public function RichLinks()
             '$1class="external" rel="external" $2<span class="nonvisual-indicator">(%s)</span>$3',
             _t(__CLASS__ . '.ExternalLink', 'external link')
         );
-        $content = preg_replace($pattern, $replacement, $content, -1);
+        $content = preg_replace($pattern ?? '', $replacement ?? '', $content ?? '', -1);
 
         return $content;
     }
diff --git a/src/PasswordEncryptor/PBKDF2.php b/src/PasswordEncryptor/PBKDF2.php
index b831628..db1fcfe 100644
--- a/src/PasswordEncryptor/PBKDF2.php
+++ b/src/PasswordEncryptor/PBKDF2.php
@@ -44,6 +44,11 @@ public function getIterations(): int
 
     public function encrypt($password, $salt = null, $member = null)
     {
-        return hash_pbkdf2($this->getAlgorithm(), (string) $password, (string) $salt, $this->getIterations());
+        return hash_pbkdf2(
+            $this->getAlgorithm() ?? '',
+            (string) $password,
+            (string) $salt,
+            $this->getIterations() ?? 0
+        );
     }
 }
diff --git a/tests/PasswordEncryptor/PBKDF2Test.php b/tests/PasswordEncryptor/PBKDF2Test.php
index f491e42..e69fc24 100644
--- a/tests/PasswordEncryptor/PBKDF2Test.php
+++ b/tests/PasswordEncryptor/PBKDF2Test.php
@@ -21,7 +21,7 @@ public function testEncrypt()
         $result = $encryptor->encrypt('opensesame', $salt);
         $this->assertSame(
             '6bafcacb90',
-            substr($result, 0, 10),
+            substr($result ?? '', 0, 10),
             'Hashed password with predictable salt did not match fixtured expectation'
         );
     }