diff --git a/client/core/src/lib/validator.js b/client/core/src/lib/validator.js
index 9f8d6d53f..e1a3dd1ed 100644
--- a/client/core/src/lib/validator.js
+++ b/client/core/src/lib/validator.js
@@ -72,9 +72,11 @@ export function validateAll(value, validations) {
 export function validate(value, conf) {
     let validator = validators[conf.validation];
     try {
-        checkNull(value, conf);
+        let isEmpty = value == null || value === '';
 
-        if (validator) // && value != null ??
+        if (isEmpty)
+            checkNull(value, conf);
+        if (validator && (!isEmpty || conf.validation == 'presence'))
             validator(value, conf);
     } catch (e) {
         let message = conf.message ? conf.message : e.message;
diff --git a/services/loopback/common/models/client.js b/services/loopback/common/models/client.js
index 2b21ccfa3..a6391e91e 100644
--- a/services/loopback/common/models/client.js
+++ b/services/loopback/common/models/client.js
@@ -43,7 +43,9 @@ module.exports = function(Self) {
 
     var validateIban = require('../validations/validateIban');
     Self.validateBinded('iban', validateIban, {
-        message: 'El iban no tiene el formato correcto'
+        message: 'El iban no tiene el formato correcto',
+        allowNull: true, // FIXME: Ignored by loopback when it's false
+        allowBlank: true
     });
 
     let validateDni = require('../validations/validateDni');
diff --git a/services/loopback/common/validations/validateDni.js b/services/loopback/common/validations/validateDni.js
index c30890c6e..150603b7f 100644
--- a/services/loopback/common/validations/validateDni.js
+++ b/services/loopback/common/validations/validateDni.js
@@ -1,6 +1,6 @@
-module.exports = fiWithCountry => {
-    if (fiWithCountry == null)
-        return true;
+module.exports = function(fiWithCountry) {
+    if (fiWithCountry == null) return true;
+    if (typeof fiWithCountry != 'string') return false;
 
     fiWithCountry = fiWithCountry.toUpperCase();