diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index 460a6b8038..e9ab7f37b1 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -5102,6 +5102,10 @@ function sanitize_textarea_field( $str ) {
  * @return string Sanitized string.
  */
 function _sanitize_text_fields( $str, $keep_newlines = false ) {
+	if ( ! is_string( $str ) ) {
+		return '';
+	}
+
 	$filtered = wp_check_invalid_utf8( $str );
 
 	if ( strpos( $filtered, '<' ) !== false ) {
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 9f22cd2881..5f33d63dc1 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-beta1-44617';
+$wp_version = '5.1-beta1-44618';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.