diff --git a/core/CliMulti/Process.php b/core/CliMulti/Process.php
index 0985b207379..b1dbb1e3fc7 100644
--- a/core/CliMulti/Process.php
+++ b/core/CliMulti/Process.php
@@ -311,7 +311,7 @@ public static function getListOfRunningProcesses()
      */
     public static function getRunningProcesses()
     {
-        $ids = explode("\n", trim(shell_exec(self::PS_COMMAND . ' 2>/dev/null | ' . self::AWK_COMMAND . ' 2>/dev/null')));
+        $ids = explode("\n", trim(shell_exec(self::PS_COMMAND . ' 2>/dev/null | ' . self::AWK_COMMAND . ' 2>/dev/null') ?? ''));
 
         $ids = array_map('intval', $ids);
         $ids = array_filter($ids, function ($id) {
diff --git a/core/Filechecks.php b/core/Filechecks.php
index cd3264002fe..d7b3b651852 100644
--- a/core/Filechecks.php
+++ b/core/Filechecks.php
@@ -150,7 +150,7 @@ public static function getUserAndGroup()
             return $user . ':' . $user;
         }
 
-        $group = trim(shell_exec('groups ' . $user . ' | cut -f3 -d" "'));
+        $group = trim(shell_exec('groups ' . $user . ' | cut -f3 -d" "') ?? '');
 
         if (empty($group) && function_exists('posix_getegid') && function_exists('posix_getgrgid')) {
             $currentGroupId = posix_getegid();
@@ -173,7 +173,7 @@ public static function getUserAndGroup()
     public static function getUser()
     {
         if (function_exists('shell_exec')) {
-            return trim(shell_exec('whoami'));
+            return trim(shell_exec('whoami') ?? '');
         }
 
         $currentUser = get_current_user();
diff --git a/plugins/CoreConsole/Commands/GitCommit.php b/plugins/CoreConsole/Commands/GitCommit.php
index c075d473766..8701023b672 100644
--- a/plugins/CoreConsole/Commands/GitCommit.php
+++ b/plugins/CoreConsole/Commands/GitCommit.php
@@ -141,7 +141,7 @@ private function getSubmodulePaths()
     protected function getStatusOfSubmodule($submodule)
     {
         $cmd    = sprintf('cd %s/%s && git status --porcelain', PIWIK_DOCUMENT_ROOT, $submodule);
-        $status = trim(shell_exec($cmd));
+        $status = trim(shell_exec($cmd) ?? '');
 
         return $status;
     }
diff --git a/plugins/TestRunner/Commands/TestsRun.php b/plugins/TestRunner/Commands/TestsRun.php
index 8624ab31b8a..118aa15b6ff 100644
--- a/plugins/TestRunner/Commands/TestsRun.php
+++ b/plugins/TestRunner/Commands/TestsRun.php
@@ -87,7 +87,7 @@ function ($xdebugFile) {
 
             $output->writeln("<info>using $xdebugFile as xdebug extension.</info>");
 
-            $phpunitPath = trim(shell_exec('which phpunit'));
+            $phpunitPath = trim(shell_exec('which phpunit') ?? '');
 
             $command = sprintf('php -d zend_extension=%s %s', $xdebugFile, $phpunitPath);
         }