diff --git a/core/lib/Drupal/Core/Config/Schema/Mapping.php b/core/lib/Drupal/Core/Config/Schema/Mapping.php
index 5729390..a85fac4 100644
--- a/core/lib/Drupal/Core/Config/Schema/Mapping.php
+++ b/core/lib/Drupal/Core/Config/Schema/Mapping.php
@@ -27,22 +27,18 @@ class Mapping extends ArrayElement implements ComplexDataInterface {
   protected $propertyDefinitions;
 
   /**
-   * Overrides ArrayElement::parse()
-   *
-   * Note this only returns elements that have a data definition.
+   * {@inheritdoc}
    */
   protected function parse() {
     $elements = array();
     foreach ($this->getPropertyDefinitions() as $key => $definition) {
-      if (isset($this->value[$key]) || array_key_exists($key, $this->value)) {
-        $elements[$key] = $this->parseElement($key, $this->value[$key], $definition);
-      }
+      $elements[$key] = $this->parseElement($key, $this->value[$key], $definition);
     }
     return $elements;
   }
 
   /**
-   * Implements Drupal\Core\TypedData\ComplexDataInterface::get().
+   * {@inheritdoc}
    *
    * Since all configuration objects are mappings the function will except a dot
    * delimited key to access nested values, for example, 'page.front'.
@@ -53,19 +49,22 @@ public function get($property_name) {
     $elements = $this->getElements();
     if (isset($elements[$root_key])) {
       $element = $elements[$root_key];
+      // If $property_name contained a dot recurse into the keys.
+      while ($element && ($key = array_shift($parts)) !== NULL) {
+        if (method_exists($element, 'get')) {
+          $element = $element->get($key);
+        }
+        else {
+          $element = NULL;
+        }
+      }
     }
-    else {
-      throw new SchemaIncompleteException(String::format("The configuration property @key doesn't exist.", array('@key' => $property_name)));
+    if (isset($element)) {
+      return $element;
     }
-
-    // If $property_name contained a dot recurse into the keys.
-    foreach ($parts as $key) {
-     if (!is_object($element) || !method_exists($element, 'get')) {
-        throw new SchemaIncompleteException(String::format("The configuration property @key does not exist.", array('@key' => $property_name)));
-      }
-      $element = $element->get($key);
+    else {
+      throw new \InvalidArgumentException(String::format("The configuration property @key doesn't exist.", array('@key' => $property_name)));
     }
-    return $element;
   }
 
   /**
@@ -130,9 +129,9 @@ public function getPropertyDefinition($name) {
   public function getPropertyDefinitions() {
     if (!isset($this->propertyDefinitions)) {
       $this->propertyDefinitions = array();
-      foreach ($this->definition['mapping'] as $key => $definition) {
-        $value = isset($this->value[$key]) ? $this->value[$key] : NULL;
-        $this->propertyDefinitions[$key] = $this->buildDataDefinition($definition, $value, $key);
+      foreach ($this->getAllKeys() as $key) {
+        $definition = isset($this->definition['mapping'][$key]) ? $this->definition['mapping'][$key] : array();
+        $this->propertyDefinitions[$key] = $this->buildDataDefinition($definition, $this->value[$key], $key);
       }
     }
     return $this->propertyDefinitions;
diff --git a/core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php b/core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php
index 4348316..0836eaf 100644
--- a/core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php
+++ b/core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php
@@ -78,15 +78,11 @@ public function checkConfigSchema(TypedConfigManagerInterface $typed_config, $co
    */
   protected function checkValue($key, $value) {
     $error_key = $this->configName . ':' . $key;
-    $element = FALSE;
-    try {
-      $element = $this->schema->get($key);
-    }
-    catch (SchemaIncompleteException $e) {
-      if (is_scalar($value) || $value === NULL) {
-        return array($error_key => 'Missing schema');
-      }
+    $element = $this->schema->get($key);
+    if ($element instanceof Undefined) {
+      return array($error_key => 'Missing schema.');
     }
+
     // Do not check value if it is defined to be ignored.
     if ($element && $element instanceof Ignore) {
       return array();
@@ -112,7 +108,7 @@ protected function checkValue($key, $value) {
     else {
       $errors = array();
       if (!$element instanceof ArrayElement) {
-        $errors[$error_key] = 'Non-scalar value but not defined as an array (such as mapping or sequence)';
+        $errors[$error_key] = 'Non-scalar value but not defined as an array (such as mapping or sequence).';
       }
 
       // Go on processing so we can get errors on all levels. Any non-scalar
diff --git a/core/lib/Drupal/Core/Config/StorableConfigBase.php b/core/lib/Drupal/Core/Config/StorableConfigBase.php
index b2610f7..24bc4d2 100644
--- a/core/lib/Drupal/Core/Config/StorableConfigBase.php
+++ b/core/lib/Drupal/Core/Config/StorableConfigBase.php
@@ -9,7 +9,6 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Core\Config\Schema\Ignore;
-use Drupal\Core\Config\Schema\SchemaIncompleteException;
 use Drupal\Core\TypedData\PrimitiveInterface;
 use Drupal\Core\TypedData\Type\FloatInterface;
 use Drupal\Core\TypedData\Type\IntegerInterface;
@@ -170,16 +169,7 @@ protected function validateValue($key, $value) {
    *   Exception on unsupported/undefined data type deducted.
    */
   protected function castValue($key, $value) {
-    $element = FALSE;
-    try {
-      $element = $this->getSchemaWrapper()->get($key);
-    }
-    catch (SchemaIncompleteException $e) {
-      // @todo Consider making schema handling more strict by throwing
-      // SchemaIncompleteException for all incomplete schema conditions *and*
-      // throwing it forward. See https://drupal.org/node/2183983.
-      // Until then, we need to handle the Undefined case below.
-    }
+    $element = $this->getSchemaWrapper()->get($key);
     // Do not cast value if it is unknown or defined to be ignored.
     if ($element && ($element instanceof Undefined || $element instanceof Ignore)) {
       return $value;
diff --git a/core/modules/config/src/Tests/SchemaCheckTraitTest.php b/core/modules/config/src/Tests/SchemaCheckTraitTest.php
index 3b5793a..5620422 100644
--- a/core/modules/config/src/Tests/SchemaCheckTraitTest.php
+++ b/core/modules/config/src/Tests/SchemaCheckTraitTest.php
@@ -64,12 +64,15 @@ public function testTrait() {
     $ret = $this->checkConfigSchema($this->typedConfig, 'config_test.types', $config_data);
     $this->assertIdentical($ret, TRUE);
 
-    // Add a new key and new array to test the error messages.
+    // Add a new key, a new array and overwrite boolean with array to test the
+    // error messages.
     $config_data = array('new_key' => 'new_value', 'new_array' => array()) + $config_data;
+    $config_data['boolean'] = array();
     $ret = $this->checkConfigSchema($this->typedConfig, 'config_test.types', $config_data);
     $expected = array(
-      'config_test.types:new_key' => 'Missing schema',
-      'config_test.types:new_array' => 'Non-scalar value but not defined as an array (such as mapping or sequence)',
+      'config_test.types:new_key' => 'Missing schema.',
+      'config_test.types:new_array' => 'Missing schema.',
+      'config_test.types:boolean' => 'Non-scalar value but not defined as an array (such as mapping or sequence).',
     );
     $this->assertIdentical($ret, $expected);
   }
diff --git a/core/modules/link/src/Tests/LinkFieldTest.php b/core/modules/link/src/Tests/LinkFieldTest.php
index 1a5f155..99976bc 100644
--- a/core/modules/link/src/Tests/LinkFieldTest.php
+++ b/core/modules/link/src/Tests/LinkFieldTest.php
@@ -376,10 +376,10 @@ function testLinkFormatter() {
       'rel' => array(NULL, 'nofollow'),
       'target' => array(NULL, '_blank'),
       'url_only' => array(
-        array('url_only' => array(FALSE)),
-        array('url_only' => array(FALSE), 'url_plain' => TRUE),
-        array('url_only' => array(TRUE)),
-        array('url_only' => array(TRUE), 'url_plain' => TRUE),
+        array('url_only' => FALSE),
+        array('url_only' => FALSE, 'url_plain' => TRUE),
+        array('url_only' => TRUE),
+        array('url_only' => TRUE, 'url_plain' => TRUE),
       ),
     );
     foreach ($options as $setting => $values) {
diff --git a/core/modules/migrate_drupal/src/Tests/d6/MigrateConfigSchemaBase.php b/core/modules/migrate_drupal/src/Tests/d6/MigrateConfigSchemaBase.php
index 7af563f..b5d0a3e 100644
--- a/core/modules/migrate_drupal/src/Tests/d6/MigrateConfigSchemaBase.php
+++ b/core/modules/migrate_drupal/src/Tests/d6/MigrateConfigSchemaBase.php
@@ -8,11 +8,11 @@
 namespace Drupal\migrate_drupal\Tests\d6;
 
 use Drupal\Core\Config\Schema\ArrayElement;
+use Drupal\Core\Config\Schema\Undefined;
 use Drupal\Core\Config\TypedConfigManagerInterface;
 use Drupal\Core\TypedData\Type\BooleanInterface;
 use Drupal\Core\TypedData\Type\StringInterface;
 use Drupal\Component\Utility\String;
-use Drupal\Core\Config\Schema\SchemaIncompleteException;
 use Drupal\Core\TypedData\PrimitiveInterface;
 use Drupal\Core\TypedData\Type\FloatInterface;
 use Drupal\Core\TypedData\Type\IntegerInterface;
@@ -85,14 +85,10 @@ public function assertConfigSchema(TypedConfigManagerInterface $typed_config, $c
    *   Returns mixed value.
    */
   protected function checkValue($key, $value) {
-    $element = FALSE;
-    try {
-      $element = $this->schema->get($key);
-    }
-    catch (SchemaIncompleteException $e) {
-      if (is_scalar($value) || $value === NULL) {
-        $this->fail("{$this->configName}:$key has no schema.");
-      }
+    $element = $this->schema->get($key);
+    if ($element instanceof Undefined) {
+      $this->fail("{$this->configName}:$key has no schema.");
+      return;
     }
     // Do not check value if it is defined to be ignored.
     if ($element && $element instanceof Ignore) {
diff --git a/core/modules/update/tests/modules/update_test/config/schema/update_test.schema.yml b/core/modules/update/tests/modules/update_test/config/schema/update_test.schema.yml
index 2235f2b..e7f5eef 100644
--- a/core/modules/update/tests/modules/update_test/config/schema/update_test.schema.yml
+++ b/core/modules/update/tests/modules/update_test/config/schema/update_test.schema.yml
@@ -8,8 +8,11 @@ update_test.settings:
       type: sequence
       label: 'System info'
       sequence:
-        - type: string
-          label: 'Value'
+        - type: sequence
+          label: 'Items'
+          sequence:
+            - type: string
+              label: 'Item'
     update_status:
       type: sequence
       label: 'Update status'
diff --git a/core/modules/user/config/schema/user.views.schema.yml b/core/modules/user/config/schema/user.views.schema.yml
index 55ea1c4..fc8a7fd 100644
--- a/core/modules/user/config/schema/user.views.schema.yml
+++ b/core/modules/user/config/schema/user.views.schema.yml
@@ -9,11 +9,15 @@ views.access.perm:
       label: 'Permission'
 
 views.access.role:
-  type: sequence
-  label: 'Role'
-  sequence:
-    - type: string
-      label: 'Role'
+  type: mapping
+  label: 'Roles'
+  mapping:
+    role:
+      type: sequence
+      label: 'List of roles'
+      sequence:
+        - type: string
+          label: 'Role'
 
 views.argument.user_uid:
   type: views.argument.numeric