diff --git a/wp-includes/rest-api/class-wp-rest-request.php b/wp-includes/rest-api/class-wp-rest-request.php
index d9c24e0658..73548d4f38 100644
--- a/wp-includes/rest-api/class-wp-rest-request.php
+++ b/wp-includes/rest-api/class-wp-rest-request.php
@@ -408,7 +408,7 @@ class WP_REST_Request implements ArrayAccess {
 		$order = $this->get_parameter_order();
 
 		foreach ( $order as $type ) {
-			if ( array_key_exists( $key, $this->params[ $type ] ) ) {
+			if ( is_array( $this->params[ $type ] ) && array_key_exists( $key, $this->params[ $type ] ) ) {
 				return true;
 			}
 		}
@@ -433,7 +433,7 @@ class WP_REST_Request implements ArrayAccess {
 		$found_key = false;
 
 		foreach ( $order as $type ) {
-			if ( 'defaults' !== $type && array_key_exists( $key, $this->params[ $type ] ) ) {
+			if ( 'defaults' !== $type && is_array( $this->params[ $type ] ) && array_key_exists( $key, $this->params[ $type ] ) ) {
 				$this->params[ $type ][ $key ] = $value;
 				$found_key                     = true;
 			}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 3de17a4911..7ea42a1b09 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5-beta3-48641';
+$wp_version = '5.5-beta3-48642';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.