diff --git a/src/core.js b/src/core.js
index 08352d41c..a48d55716 100644
--- a/src/core.js
+++ b/src/core.js
@@ -1025,7 +1025,7 @@ $.extend( $.validator, {
 		// meta-characters that should be escaped in order to be used with JQuery
 		// as a literal part of a name/id or any selector.
 		escapeCssMeta: function( string ) {
-			return string.replace( /([\\!"#$%&'()*+,./:;<=>?@\[\]^`{|}~])/g, "\\$1" );
+			return string ? string.replace( /([\\!"#$%&'()*+,./:;<=>?@\[\]^`{|}~])/g, "\\$1" ) : "";
 		},
 
 		idOrName: function( element ) {