diff --git a/src/app/services/validation.service.ts b/src/app/services/validation.service.ts
index bcefafa..3031ea8 100644
--- a/src/app/services/validation.service.ts
+++ b/src/app/services/validation.service.ts
@@ -50,7 +50,7 @@ export class ValidationService {
   }
 
   string(data, option = null) {
-    let validator = Joi.string().max(128).allow('');
+    let validator = Joi.string().max(128).allow('', true, false);
     let errorMsg = 'must contain max 128 characters';
     if (option === 'alphanum') {
       validator = validator.alphanum();