diff --git a/wp-includes/class-wp-theme-json-resolver.php b/wp-includes/class-wp-theme-json-resolver.php
index cf14486f67..c166283af3 100644
--- a/wp-includes/class-wp-theme-json-resolver.php
+++ b/wp-includes/class-wp-theme-json-resolver.php
@@ -246,8 +246,13 @@ class WP_Theme_JSON_Resolver {
 		$options = wp_parse_args( $options, array( 'with_supports' => true ) );
 
 		if ( null === static::$theme || ! static::has_same_registered_blocks( 'theme' ) ) {
-			$theme_json_data = static::read_json_file( static::get_file_path_from_theme( 'theme.json' ) );
-			$theme_json_data = static::translate( $theme_json_data, wp_get_theme()->get( 'TextDomain' ) );
+			$theme_json_file = static::get_file_path_from_theme( 'theme.json' );
+			if ( '' !== $theme_json_file ) {
+				$theme_json_data = static::read_json_file( $theme_json_file );
+				$theme_json_data = static::translate( $theme_json_data, wp_get_theme()->get( 'TextDomain' ) );
+			} else {
+				$theme_json_data = array();
+			}
 
 			/**
 			 * Filters the data provided by the theme for global styles and settings.
@@ -259,20 +264,23 @@ class WP_Theme_JSON_Resolver {
 			$theme_json      = apply_filters( 'wp_theme_json_data_theme', new WP_Theme_JSON_Data( $theme_json_data, 'theme' ) );
 			$theme_json_data = $theme_json->get_data();
 			static::$theme   = new WP_Theme_JSON( $theme_json_data );
-		}
 
-		if ( wp_get_theme()->parent() ) {
-			// Get parent theme.json.
-			$parent_theme_json_data = static::read_json_file( static::get_file_path_from_theme( 'theme.json', true ) );
-			$parent_theme_json_data = static::translate( $parent_theme_json_data, wp_get_theme()->parent()->get( 'TextDomain' ) );
-			$parent_theme           = new WP_Theme_JSON( $parent_theme_json_data );
+			if ( wp_get_theme()->parent() ) {
+				// Get parent theme.json.
+				$parent_theme_json_file = static::get_file_path_from_theme( 'theme.json', true );
+				if ( '' !== $parent_theme_json_file ) {
+					$parent_theme_json_data = static::read_json_file( $parent_theme_json_file );
+					$parent_theme_json_data = static::translate( $parent_theme_json_data, wp_get_theme()->parent()->get( 'TextDomain' ) );
+					$parent_theme           = new WP_Theme_JSON( $parent_theme_json_data );
 
-			/*
-			 * Merge the child theme.json into the parent theme.json.
-			 * The child theme takes precedence over the parent.
-			 */
-			$parent_theme->merge( static::$theme );
-			static::$theme = $parent_theme;
+					/*
+					 * Merge the child theme.json into the parent theme.json.
+					 * The child theme takes precedence over the parent.
+					 */
+					$parent_theme->merge( static::$theme );
+					static::$theme = $parent_theme;
+				}
+			}
 		}
 
 		if ( ! $options['with_supports'] ) {
@@ -403,6 +411,18 @@ class WP_Theme_JSON_Resolver {
 		if ( ! $theme instanceof WP_Theme ) {
 			$theme = wp_get_theme();
 		}
+
+		/*
+		 * Bail early if the theme does not support a theme.json.
+		 *
+		 * Since WP_Theme_JSON_Resolver::theme_has_support() only supports the active
+		 * theme, the extra condition for whether $theme is the active theme is
+		 * present here.
+		 */
+		if ( $theme->get_stylesheet() === get_stylesheet() && ! static::theme_has_support() ) {
+			return array();
+		}
+
 		$user_cpt         = array();
 		$post_type_filter = 'wp_global_styles';
 		$stylesheet       = $theme->get_stylesheet();
@@ -582,8 +602,8 @@ class WP_Theme_JSON_Resolver {
 	public static function theme_has_support() {
 		if ( ! isset( static::$theme_has_support ) ) {
 			static::$theme_has_support = (
-				is_readable( static::get_file_path_from_theme( 'theme.json' ) ) ||
-				is_readable( static::get_file_path_from_theme( 'theme.json', true ) )
+				static::get_file_path_from_theme( 'theme.json' ) !== '' ||
+				static::get_file_path_from_theme( 'theme.json', true ) !== ''
 			);
 		}
 
diff --git a/wp-includes/class-wp-theme-json.php b/wp-includes/class-wp-theme-json.php
index d0fcdeb52a..df5bd20d84 100644
--- a/wp-includes/class-wp-theme-json.php
+++ b/wp-includes/class-wp-theme-json.php
@@ -2939,7 +2939,8 @@ class WP_Theme_JSON {
 	public function set_spacing_sizes() {
 		$spacing_scale = _wp_array_get( $this->theme_json, array( 'settings', 'spacing', 'spacingScale' ), array() );
 
-		if ( ! is_numeric( $spacing_scale['steps'] )
+		if ( ! isset( $spacing_scale['steps'] )
+			|| ! is_numeric( $spacing_scale['steps'] )
 			|| ! isset( $spacing_scale['mediumStep'] )
 			|| ! isset( $spacing_scale['unit'] )
 			|| ! isset( $spacing_scale['operator'] )
diff --git a/wp-includes/version.php b/wp-includes/version.php
index ba059b1142..16d3aa9116 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.2-alpha-54797';
+$wp_version = '6.2-alpha-54799';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.