--- a/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/AbstractSingleItemPanel.java	Wed Jul 18 12:20:01 2018 +0200
+++ b/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/AbstractSingleItemPanel.java	Wed Jul 18 15:34:53 2018 +0200
@@ -115,9 +115,9 @@
 
     @Override
     protected final Data[] getData() {
-        final List<String> errors = this.validate();
+        final List<String> errors = this.validate(); // do not allow advance state
         if (errors.size() > 0) {
-            showErrors(errors); // TODO: do not allow advance state
+            showErrors(errors);
         }
         if (this.inputItem != null && !this.inputItem.getValueAsString().isEmpty()) {
             final List<Data> data = new ArrayList<Data>();