diff --git a/db.php b/db.php
index 6643331..d8c8788 100644
--- a/db.php
+++ b/db.php
@@ -842,6 +842,9 @@ public function set_charset( $dbh, $charset = null, $collate = null ) {
 	 * This is also the reason why we don't allow certain charsets. See set_charset().
 	 */
 	public function _real_escape( $string ) {   // phpcs:ignore PSR2.Methods.MethodDeclaration.Underscore
+		if ( is_null( $string ) ) {
+			return $string;
+		}
 		$escaped = addslashes( (string) $string );
 		if ( method_exists( get_parent_class( $this ), 'add_placeholder_escape' ) ) {
 			$escaped = $this->add_placeholder_escape( $escaped );