Index: trunk/src/wp-includes/class-wp-theme-json.php
===================================================================
--- trunk/src/wp-includes/class-wp-theme-json.php	(revision 64304)
+++ trunk/src/wp-includes/class-wp-theme-json.php	(revision 64309)
@@ -1141,5 +1141,5 @@
 		$scale_path    = array( 'settings', 'spacing', 'spacingScale' );
 		$spacing_scale = _wp_array_get( $this->theme_json, $scale_path, null );
-		if ( null !== $spacing_scale ) {
+		if ( is_array( $spacing_scale ) ) {
 			// If the spacingScale is not already keyed by origin.
 			if ( empty( array_intersect( array_keys( $spacing_scale ), static::VALID_ORIGINS ) ) ) {
@@ -1215,5 +1215,8 @@
 				$block_level_data = $new_theme_json['styles']['blocks'][ $block_type ]['variations'][ $variation_name ] ?? array();
 				$top_level_data   = $variations[ $variation_name ] ?? array();
-				$merged_data      = array_replace_recursive( $top_level_data, $block_level_data );
+				if ( ! is_array( $block_level_data ) || ! is_array( $top_level_data ) ) {
+					continue;
+				}
+				$merged_data = array_replace_recursive( $top_level_data, $block_level_data );
 				if ( ! empty( $merged_data ) ) {
 					_wp_array_set( $new_theme_json, array( 'styles', 'blocks', $block_type, 'variations', $variation_name ), $merged_data );
@@ -1494,5 +1497,5 @@
 			$variation_pseudo_selectors = array();
 			foreach ( $input['blockTypes'] as $variation_block_type ) {
-				if ( isset( static::VALID_BLOCK_PSEUDO_SELECTORS[ $variation_block_type ] ) ) {
+				if ( is_string( $variation_block_type ) && isset( static::VALID_BLOCK_PSEUDO_SELECTORS[ $variation_block_type ] ) ) {
 					$variation_pseudo_selectors = array_merge(
 						$variation_pseudo_selectors,
@@ -2102,5 +2105,8 @@
 		if ( in_array( 'custom-css', $types, true ) ) {
 			// Add the global styles root CSS.
-			$stylesheet .= _wp_array_get( $this->theme_json, array( 'styles', 'css' ) );
+			$root_css = $this->theme_json['styles']['css'] ?? '';
+			if ( is_string( $root_css ) ) {
+				$stylesheet .= $root_css;
+			}
 		}
 
@@ -2122,5 +2128,5 @@
 		$processed_css = '';
 
-		if ( empty( $css ) ) {
+		if ( empty( $css ) || ! is_string( $css ) ) {
 			return $processed_css;
 		}
@@ -3242,5 +3248,5 @@
 		 * the URL takes precedence and the ref is ignored.
 		 */
-		if ( is_array( $value ) && isset( $value['ref'] ) ) {
+		if ( is_array( $value ) && isset( $value['ref'] ) && is_string( $value['ref'] ) ) {
 			$value_path = explode( '.', $value['ref'] );
 			$ref_value  = _wp_array_get( $theme_json, $value_path );
@@ -4432,9 +4438,11 @@
 
 			// Apply the base spacing scale to the current layer.
-			$base_spacing_scale      = _wp_array_get( $this->theme_json, $scale_path, array() );
-			$flattened_spacing_scale = array_replace( $flattened_spacing_scale, $base_spacing_scale );
+			$base_spacing_scale = _wp_array_get( $this->theme_json, $scale_path, array() );
+			if ( is_array( $base_spacing_scale ) ) {
+				$flattened_spacing_scale = array_replace( $flattened_spacing_scale, $base_spacing_scale );
+			}
 
 			$spacing_scale = _wp_array_get( $incoming_data, $scale_path, null );
-			if ( ! isset( $spacing_scale ) ) {
+			if ( ! is_array( $spacing_scale ) ) {
 				continue;
 			}
@@ -5570,4 +5578,5 @@
 			! is_numeric( $spacing_scale['mediumStep'] ) ||
 			! isset( $spacing_scale['unit'] ) ||
+			! is_string( $spacing_scale['unit'] ) ||
 			! isset( $spacing_scale['operator'] ) ||
 			( '+' !== $spacing_scale['operator'] && '*' !== $spacing_scale['operator'] ) ||