SQLContainer (FreeformQuery), Table and Generated Column

Vaadin 6 / 7 / 8 Framework Data Binding
1

Hi folks,
I have new question:

I am using a Table with an SQLContainer as data source, which is filled by a FreeformQuery. This container is readonly which is okay for me, 'cause I just want to show data.
Now I want to use a generated column on one of my columns delivered by that SQL query. In that column I have float values (seconds) and want to convert them to Strings like “1m 20s”

But the ColumnGenerator does not work properly:

My generator looks like this:

GeneralData.addGeneratedColumn("min_eingehend",new Table.ColumnGenerator() {
		public Component generateCell(Table source, Object itemId, Object columnId) {
			Item item=source.getItem(itemId);
			Property prop=item.getItemProperty("Dauer eingehend");

			int min=(int)Float.parseFloat(prop.toString())/60;
			int sec=(int)Float.parseFloat(prop.toString())%60;
			return new Label(min+"m"+sec+"s");
		}
	});

In the debugger inside that Generator I get the following values for the parameter values:

this = {TelTable$3@2710}
source = {com.vaadin.ui.Table@2715}“null”
itemId = {com.vaadin.addon.sqlcontainer.ReadOnlyRowId@2717
}Method threw ‘java.lang.NullPointerException’ exception. Cannot evaluate com.vaadin.addon.sqlcontainer.ReadOnlyRowId.toString()

columnId = {java.lang.String@2718}“min_eingehend”
item = {com.vaadin.addon.sqlcontainer.RowItem@2719
}Method threw ‘java.lang.NullPointerException’ exception. Cannot evaluate com.vaadin.addon.sqlcontainer.RowItem.toString()

prop = {com.vaadin.addon.sqlcontainer.ColumnProperty@2720}“null”

where TelTable is my application.

Thanks for any ideas!?