--- a/app/model/Probe.js	Mon Mar 23 18:04:59 2015 +0100
+++ b/app/model/Probe.js	Tue Mar 24 10:40:01 2015 +0100
@@ -22,7 +22,13 @@
     }, {
         name: 'test'
     }, {
-        name: 'netzbetreiberId'
+        name: 'netzbetreiberId',
+        serialize: function(value) {
+            if (value === '') {
+                return null;
+            }
+            return value;
+        }
     }, {
         name: 'mstId'
     }, {
@@ -36,7 +42,13 @@
     }, {
         name: 'media'
     }, {
-        name: 'umwId'
+        name: 'umwId',
+        serialize: function(value) {
+            if (value === '') {
+                return null;
+            }
+            return value;
+        }
     }, {
         name: 'probeentnahmeBeginn',
         type: 'date',