diff --git a/core/lib/Drupal/Core/Config/StorableConfigBase.php b/core/lib/Drupal/Core/Config/StorableConfigBase.php
index 18c0f07..a72ddf6 100644
--- a/core/lib/Drupal/Core/Config/StorableConfigBase.php
+++ b/core/lib/Drupal/Core/Config/StorableConfigBase.php
@@ -12,6 +12,7 @@
 use Drupal\Core\TypedData\PrimitiveInterface;
 use Drupal\Core\TypedData\Type\FloatInterface;
 use Drupal\Core\TypedData\Type\IntegerInterface;
+use Drupal\Core\Config\Schema\Property;
 
 /**
  * Provides a base class for configuration objects with storage support.
@@ -167,36 +168,31 @@ protected function validateValue($key, $value) {
    *   Exception on unsupported/undefined data type deducted.
    */
   protected function castValue($key, $value) {
-    if ($value === NULL) {
-      $value = NULL;
+    $element = FALSE;
+    try {
+      $element = $this->getSchemaWrapper()->get($key);
     }
-    elseif (is_scalar($value)) {
-      try {
-        $element = $this->getSchemaWrapper()->get($key);
-        if ($element instanceof PrimitiveInterface) {
-          // Special handling for integers and floats since the configuration
-          // system is primarily concerned with saving values from the Form API
-          // we have to special case the meaning of an empty string for numeric
-          // types. In PHP this would be casted to a 0 but for the purposes of
-          // configuration we need to treat this as a NULL.
-          if ($value === '' && ($element instanceof IntegerInterface || $element instanceof FloatInterface)) {
-            $value = NULL;
-          }
-          else {
-            $value = $element->getCastedValue();
-          }
-        }
-        else {
-          // Config only supports primitive data types. If the config schema
-          // does define a type $element will be an instance of
-          // \Drupal\Core\Config\Schema\Property. Convert it to string since it
-          // is the safest possible type.
-          $value = $element->getString();
-        }
+    catch (SchemaIncompleteException $e) {
+      // @todo throw an exception due to an incomplete schema.
+      // Fix as part of https://drupal.org/node/2183983.
+    }
+    // Do not cast value of a property, as it is unknown or mixed.
+    if ($element && $element instanceof Property) {
+      return $value;
+    }
+    if ((is_scalar($value) || $value === NULL) && ($element && $element instanceof PrimitiveInterface)) {
+      // Special handling for integers and floats since the configuration
+      // system is primarily concerned with saving values from the Form API
+      // we have to special case the meaning of an empty string for numeric
+      // types. In PHP this would be casted to a 0 but for the purposes of
+      // configuration we need to treat this as a NULL.
+      $empty_value =  $value === '' && ($element instanceof IntegerInterface || $element instanceof FloatInterface);
+
+      if ($value === NULL || $empty_value) {
+        $value = NULL;
       }
-      catch (SchemaIncompleteException $e) {
-        // @todo throw an exception due to an incomplete schema.
-        // Fix as part of https://drupal.org/node/2183983.
+      else {
+        $value = $element->getCastedValue();
       }
     }
     else {
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTestBase.php b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTestBase.php
index c490490..ce9aa63 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTestBase.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTestBase.php
@@ -101,6 +101,7 @@ protected function checkValue($key, $value) {
         $this->fail("{$this->configName}:$key has no schema.");
       }
     }
+    // Do not check value of property, as it is unknown or mixed.
     if ($element && $element instanceof Property) {
       return $value;
     }