diff -r c7c34916027a -r 177826044cd9 wp/wp-includes/customize/class-wp-customize-custom-css-setting.php
--- a/wp/wp-includes/customize/class-wp-customize-custom-css-setting.php	Mon Oct 14 18:06:33 2019 +0200
+++ b/wp/wp-includes/customize/class-wp-customize-custom-css-setting.php	Mon Oct 14 18:28:13 2019 +0200
@@ -127,8 +127,8 @@
 			}
 		}
 		$id_base = $this->id_data['base'];
-		$value = '';
-		$post = wp_get_custom_css_post( $this->stylesheet );
+		$value   = '';
+		$post    = wp_get_custom_css_post( $this->stylesheet );
 		if ( $post ) {
 			$value = $post->post_content;
 		}
@@ -161,7 +161,7 @@
 			$validity->add( 'illegal_markup', __( 'Markup is not allowed in CSS.' ) );
 		}
 
-		if ( empty( $validity->errors ) ) {
+		if ( ! $validity->has_errors() ) {
 			$validity = parent::validate( $css );
 		}
 		return $validity;
@@ -180,9 +180,12 @@
 			$css = '';
 		}
 
-		$r = wp_update_custom_css_post( $css, array(
-			'stylesheet' => $this->stylesheet,
-		) );
+		$r = wp_update_custom_css_post(
+			$css,
+			array(
+				'stylesheet' => $this->stylesheet,
+			)
+		);
 
 		if ( $r instanceof WP_Error ) {
 			return false;