diff --git a/src/Illuminate/Console/Scheduling/CallbackEvent.php b/src/Illuminate/Console/Scheduling/CallbackEvent.php
index e91600ac3a40..db5e0297072a 100644
--- a/src/Illuminate/Console/Scheduling/CallbackEvent.php
+++ b/src/Illuminate/Console/Scheduling/CallbackEvent.php
@@ -184,7 +184,7 @@ public function getSummaryForDisplay()
      */
     public function mutexName()
     {
-        return 'framework/schedule-'.sha1($this->description);
+        return 'framework/schedule-'.sha1($this->description ?? '');
     }
 
     /**
diff --git a/src/Illuminate/Console/Scheduling/ScheduleListCommand.php b/src/Illuminate/Console/Scheduling/ScheduleListCommand.php
index 027da980af38..2138a5a92e8c 100644
--- a/src/Illuminate/Console/Scheduling/ScheduleListCommand.php
+++ b/src/Illuminate/Console/Scheduling/ScheduleListCommand.php
@@ -83,7 +83,7 @@ public function handle(Schedule $schedule)
             $command = $event->command;
             $description = $event->description;
 
-            if (! $this->output->isVerbose() && ! is_null($command)) {
+            if (! $this->output->isVerbose() && is_string($command)) {
                 $command = str_replace([Application::phpBinary(), Application::artisanBinary()], [
                     'php',
                     preg_replace("#['\"]#", '', Application::artisanBinary()),
@@ -91,7 +91,7 @@ public function handle(Schedule $schedule)
             }
 
             if ($event instanceof CallbackEvent) {
-                if (! is_null($event->description) && class_exists($event->description)) {
+                if (is_string($event->description) && class_exists($event->description)) {
                     $command = $event->description;
                     $description = '';
                 } else {