diff --git a/wp-includes/class-wp-customize-manager.php b/wp-includes/class-wp-customize-manager.php
index 4d7bf3ba44..be369a1cb3 100644
--- a/wp-includes/class-wp-customize-manager.php
+++ b/wp-includes/class-wp-customize-manager.php
@@ -5098,10 +5098,10 @@ final class WP_Customize_Manager {
 					'label'         => __( 'Logo' ),
 					'section'       => 'title_tagline',
 					'priority'      => 8,
-					'height'        => $custom_logo_args[0]['height'],
-					'width'         => $custom_logo_args[0]['width'],
-					'flex_height'   => $custom_logo_args[0]['flex-height'],
-					'flex_width'    => $custom_logo_args[0]['flex-width'],
+					'height'        => isset( $custom_logo_args[0]['height'] ) ? $custom_logo_args[0]['height'] : null,
+					'width'         => isset( $custom_logo_args[0]['width'] ) ? $custom_logo_args[0]['width'] : null,
+					'flex_height'   => isset( $custom_logo_args[0]['flex-height'] ) ? $custom_logo_args[0]['flex-height'] : null,
+					'flex_width'    => isset( $custom_logo_args[0]['flex-width'] ) ? $custom_logo_args[0]['flex-width'] : null,
 					'button_labels' => array(
 						'select'       => __( 'Select logo' ),
 						'change'       => __( 'Change logo' ),
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php b/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php
index bccf1d9388..5f66023b43 100644
--- a/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php
+++ b/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php
@@ -477,8 +477,11 @@ class WP_Customize_Nav_Menu_Item_Setting extends WP_Customize_Setting {
 	 */
 	public function filter_wp_get_nav_menu_items( $items, $menu, $args ) {
 		$this_item                = $this->value();
-		$current_nav_menu_term_id = $this_item['nav_menu_term_id'];
-		unset( $this_item['nav_menu_term_id'] );
+		$current_nav_menu_term_id = null;
+		if ( isset( $this_item['nav_menu_term_id'] ) ) {
+			$current_nav_menu_term_id = $this_item['nav_menu_term_id'];
+			unset( $this_item['nav_menu_term_id'] );
+		}
 
 		$should_filter = (
 			$menu->term_id === $this->original_nav_menu_term_id
@@ -493,7 +496,7 @@ class WP_Customize_Nav_Menu_Item_Setting extends WP_Customize_Setting {
 		$should_remove = (
 			false === $this_item
 			||
-			true === $this_item['_invalid']
+			( isset( $this_item['_invalid'] ) && true === $this_item['_invalid'] )
 			||
 			(
 				$this->original_nav_menu_term_id === $menu->term_id
diff --git a/wp-includes/meta.php b/wp-includes/meta.php
index 5446c16d3e..9bd989540c 100644
--- a/wp-includes/meta.php
+++ b/wp-includes/meta.php
@@ -523,7 +523,11 @@ function get_metadata( $meta_type, $object_id, $meta_key = '', $single = false )
 
 	if ( ! $meta_cache ) {
 		$meta_cache = update_meta_cache( $meta_type, array( $object_id ) );
-		$meta_cache = $meta_cache[ $object_id ];
+		if ( isset( $meta_cache[ $object_id ] ) ) {
+			$meta_cache = $meta_cache[ $object_id ];
+		} else {
+			$meta_cache = null;
+		}
 	}
 
 	if ( ! $meta_key ) {
diff --git a/wp-includes/rest-api/class-wp-rest-request.php b/wp-includes/rest-api/class-wp-rest-request.php
index ee106b5c5a..3089547ce7 100644
--- a/wp-includes/rest-api/class-wp-rest-request.php
+++ b/wp-includes/rest-api/class-wp-rest-request.php
@@ -294,7 +294,9 @@ class WP_REST_Request implements ArrayAccess {
 	 *
 	 * @since 4.4.0
 	 *
-	 * @return array Map containing 'value' and 'parameters' keys.
+	 * @return array|null Map containing 'value' and 'parameters' keys
+	 *                    or null when no valid content-type header was
+	 *                    available.
 	 */
 	public function get_content_type() {
 		$value = $this->get_header( 'content-type' );
@@ -334,7 +336,7 @@ class WP_REST_Request implements ArrayAccess {
 		$order = array();
 
 		$content_type = $this->get_content_type();
-		if ( $content_type['value'] === 'application/json' ) {
+		if ( isset( $content_type['value'] ) && 'application/json' === $content_type['value'] ) {
 			$order[] = 'JSON';
 		}
 
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index f7f061d351..eddd76684a 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -2371,14 +2371,14 @@ function add_theme_support( $feature, ...$args ) {
 			 * Merge post types with any that already declared their support
 			 * for post thumbnails.
 			 */
-			if ( is_array( $args[0] ) && isset( $_wp_theme_features['post-thumbnails'] ) ) {
+			if ( isset( $args[0] ) && is_array( $args[0] ) && isset( $_wp_theme_features['post-thumbnails'] ) ) {
 				$args[0] = array_unique( array_merge( $_wp_theme_features['post-thumbnails'][0], $args[0] ) );
 			}
 
 			break;
 
 		case 'post-formats':
-			if ( is_array( $args[0] ) ) {
+			if ( isset( $args[0] ) && is_array( $args[0] ) ) {
 				$post_formats = get_post_format_slugs();
 				unset( $post_formats['standard'] );
 
@@ -2391,7 +2391,7 @@ function add_theme_support( $feature, ...$args ) {
 			if ( empty( $args[0] ) ) {
 				// Build an array of types for back-compat.
 				$args = array( 0 => array( 'comment-list', 'comment-form', 'search-form' ) );
-			} elseif ( ! is_array( $args[0] ) ) {
+			} elseif ( ! isset( $args[0] ) || ! is_array( $args[0] ) ) {
 				_doing_it_wrong( "add_theme_support( 'html5' )", __( 'You need to pass an array of types.' ), '3.6.1' );
 				return false;
 			}
@@ -2403,7 +2403,7 @@ function add_theme_support( $feature, ...$args ) {
 			break;
 
 		case 'custom-logo':
-			if ( ! is_array( $args ) ) {
+			if ( true === $args ) {
 				$args = array( 0 => array() );
 			}
 			$defaults = array(
@@ -2426,7 +2426,7 @@ function add_theme_support( $feature, ...$args ) {
 			return add_theme_support( 'custom-header', array( 'uploads' => true ) );
 
 		case 'custom-header':
-			if ( ! is_array( $args ) ) {
+			if ( true === $args ) {
 				$args = array( 0 => array() );
 			}
 
@@ -2516,7 +2516,7 @@ function add_theme_support( $feature, ...$args ) {
 			break;
 
 		case 'custom-background':
-			if ( ! is_array( $args ) ) {
+			if ( true === $args ) {
 				$args = array( 0 => array() );
 			}
 
diff --git a/wp-includes/user.php b/wp-includes/user.php
index 3d2bf939d4..fab14519df 100644
--- a/wp-includes/user.php
+++ b/wp-includes/user.php
@@ -2088,7 +2088,10 @@ All at ###SITENAME###
 			$logged_in_cookie = wp_parse_auth_cookie( '', 'logged_in' );
 			/** This filter is documented in wp-includes/pluggable.php */
 			$default_cookie_life = apply_filters( 'auth_cookie_expiration', ( 2 * DAY_IN_SECONDS ), $ID, false );
-			$remember            = ( ( $logged_in_cookie['expiration'] - time() ) > $default_cookie_life );
+			$remember            = false;
+			if ( false !== $logged_in_cookie && ( $logged_in_cookie['expiration'] - time() ) > $default_cookie_life ) {
+				$remember = true;
+			}
 
 			wp_set_auth_cookie( $ID, $remember );
 		}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 1a5e5afc20..5b5465c157 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45638';
+$wp_version = '5.3-alpha-45639';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-includes/wp-db.php b/wp-includes/wp-db.php
index 232b3e8ac9..4f8223fc4b 100644
--- a/wp-includes/wp-db.php
+++ b/wp-includes/wp-db.php
@@ -3113,7 +3113,7 @@ class wpdb {
 			foreach ( $data as $col => $value ) {
 				if ( ! empty( $value['db'] ) ) {
 					// We're going to need to truncate by characters or bytes, depending on the length value we have.
-					if ( 'byte' === $value['length']['type'] ) {
+					if ( isset( $value['length']['type'] ) && 'byte' === $value['length']['type'] ) {
 						// Using binary causes LEFT() to truncate by bytes.
 						$charset = 'binary';
 					} else {