XNAT-4242: Validation type that would *optionally* allow empty fields, would...

XNAT-4242: Validation type that would *optionally* allow empty fields, would instead *require* them to be empty.

src/main/webapp/scripts/xnat/validate.js

@@ -536,6 +536,7 @@ var XNAT = getObject(XNAT);
         // set 'allowEmpty' flag
         if (type === 'allow-empty') {
             this.allowEmpty = true;
+            return this;
         }
 
         if (typeof type === 'string') {