--- a/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/AbstractSingleItemPanel.java	Mon Jul 16 08:43:07 2018 +0200
+++ b/gwt-client/src/main/java/org/dive4elements/river/client/client/ui/AbstractSingleItemPanel.java	Tue Jul 17 10:59:27 2018 +0200
@@ -118,7 +118,6 @@
         final List<String> errors = this.validate();
         if (errors.size() > 0) {
             showErrors(errors); // TODO: do not allow advance state
-            // return null;
         }
         if (this.inputItem != null && !this.inputItem.getValueAsString().isEmpty()) {
             final List<Data> data = new ArrayList<Data>();
@@ -136,16 +135,6 @@
         return this.inputItem;
     }
 
-    private final List<String> checkForEmpty() {
-        final List<String> errors = new ArrayList<String>();
-
-        if (this.inputItem.getValueAsString() == null || this.inputItem.getValueAsString().trim().isEmpty()) {
-            errors.add(this.MSG.empty_filter());
-            return errors;
-        }
-        return errors;
-    }
-
     protected abstract String errorForItemMsg();
 
     protected final void appendValue(final String value) {
@@ -155,7 +144,7 @@
     @Override
     public final List<String> validate() {
         final List<String> errors = new ArrayList<String>();
-        errors.addAll(this.checkForEmpty());
+        errors.addAll(ValidationHelper.checkForEmpty(this.inputItem, this.MSG));
         final String sValue = this.inputItem.getValueAsString();
         return this.behaviour.validate(errors, sValue);
     }