diff --git a/src/main/java/org/gcube/portlets/user/td/expressionwidget/client/ColumnFilterDialog.java b/src/main/java/org/gcube/portlets/user/td/expressionwidget/client/ColumnFilterDialog.java
index aa72b96..b51d049 100644
--- a/src/main/java/org/gcube/portlets/user/td/expressionwidget/client/ColumnFilterDialog.java
+++ b/src/main/java/org/gcube/portlets/user/td/expressionwidget/client/ColumnFilterDialog.java
@@ -80,9 +80,13 @@ public class ColumnFilterDialog extends Window {
 				|| column.getTypeCode().compareTo(
 						ColumnTypeCode.MEASURE.toString()) == 0) {
 			columnExpressionPanel = new ColumnExpressionPanel(this, column);
-			columnExpressionPanel.getBtnSave().setVisible(false);
-			columnExpressionPanel.getBtnSearch().setVisible(false);
-			add(columnExpressionPanel); 
+			add(columnExpressionPanel);
+			if(columnExpressionPanel.getBtnSave()!=null){
+				columnExpressionPanel.getBtnSave().setVisible(false);
+			}
+			if(columnExpressionPanel.getBtnSearch()!=null){
+				columnExpressionPanel.getBtnSearch().setVisible(false);
+			}
 		} else {
 			HTML errorMessage = new HTML(
 					"This type of column is not supported for now!");