diff --git a/library/Director/CustomVariable/CustomVariable.php b/library/Director/CustomVariable/CustomVariable.php
index 4a824cf4..006bed11 100644
--- a/library/Director/CustomVariable/CustomVariable.php
+++ b/library/Director/CustomVariable/CustomVariable.php
@@ -118,6 +118,10 @@ abstract class CustomVariable implements IcingaConfigRenderer
 
     public static function create($key, $value)
     {
+        if (is_null($value)) {
+            return new CustomVariableNull($key, $value);
+        }
+
         if (is_string($value)) {
 
             return new CustomVariableString($key, $value);
@@ -137,7 +141,7 @@ abstract class CustomVariable implements IcingaConfigRenderer
             return new CustomVariableDictionary($key, $value);
 
         } else {
-            throw new ProgrammingError();
+            throw new ProgrammingError('WTF (%s): %s', $key, var_export($value, 1));
         }
     }
 
diff --git a/library/Director/CustomVariable/CustomVariableNull.php b/library/Director/CustomVariable/CustomVariableNull.php
new file mode 100644
index 00000000..2b190cc2
--- /dev/null
+++ b/library/Director/CustomVariable/CustomVariableNull.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace Icinga\Module\Director\CustomVariable;
+
+use Icinga\Module\Director\IcingaConfig\IcingaConfigHelper as c;
+use Icinga\Exception\ProgrammingError;
+
+class CustomVariableNull extends CustomVariable
+{
+    public function equals(CustomVariable $var)
+    {
+        return $var->getValue() === $this->getValue();
+    }
+
+    public function getValue()
+    {
+        return null;
+    }
+
+    public function setValue($value)
+    {
+        if (! is_null($value)) {
+            throw new ProgrammingError(
+                'Null can only be null, got %s',
+                var_export($value, 1)
+            );
+        }
+
+        return $this;
+    } 
+
+    public function toConfigString()
+    {
+        return 'null';
+    }
+}