Update to Drupal 8.0.0-rc3. For more information, see https://www.drupal.org/node/2608078

core/modules/block/src/BlockViewBuilder.php

@@ -186,8 +186,6 @@ class BlockViewBuilder extends EntityViewBuilder {
    *   A block config entity ID.
    * @param $view_mode
    *   The view mode the block is being viewed in.
-   * @param $langcode
-   *   The langcode the block is being viewed in.
    *
    * @return array
    *   A render array with a #pre_render callback to render the block.

core/modules/block/src/Tests/BlockUiTest.php

@@ -207,7 +207,6 @@ class BlockUiTest extends WebTestBase {
     $this->assertTrue(!empty($elements), 'The context-aware test block appears.');
     $definition = \Drupal::service('plugin.manager.block')->getDefinition('test_context_aware');
     $this->assertTrue(!empty($definition), 'The context-aware test block exists.');
-
     $edit = [
       'region' => 'content',
       'settings[context_mapping][user]' => '@block_test.multiple_static_context:user2',
@@ -217,6 +216,15 @@ class BlockUiTest extends WebTestBase {
     $this->drupalGet('');
     $this->assertText('Test context-aware block');
     $this->assertRaw($expected_text);
+
+    // Test context mapping allows empty selection for optional contexts.
+    $this->drupalGet('admin/structure/block/manage/testcontextawareblock');
+    $edit = [
+      'settings[context_mapping][user]' => '',
+    ];
+    $this->drupalPostForm(NULL, $edit, 'Save block');
+    $this->drupalGet('');
+    $this->assertText('No context mapping selected.');
   }
 
   /**

core/modules/block/src/Tests/Migrate/d6/MigrateBlockTest.php

@@ -61,8 +61,6 @@ class MigrateBlockTest extends MigrateDrupal6TestBase {
    *
    * @param string $id
    *   The block ID.
-   * @param string $module
-   *   The module.
    * @param array $visibility
    *   The block visibility settings.
    * @param string $region