Failing multiple field validation in SmartGWT

I am trying to have a form field contain one or more elements that are defined in a different data source. Elements have a numeric id and a human-readable name. It all works well until I try to save; in this case, I always get the "Not a valid option" error.

The form I am editing is based on a Campaigns datasource, that may be linked to zero or more Trunks.

Datasource Trunks are defined as:

    DataSourceField fId = new DataSourceField(
            "trunkId", FieldType.INTEGER, "Id");
    fId.setPrimaryKey(Boolean.TRUE);
    fId.setHidden(Boolean.TRUE);
    fId.setCanEdit(Boolean.FALSE);

    DataSourceField fName = new DataSourceField(
            "trunkName", FieldType.TEXT, "Name");
    fName.setRequired(Boolean.TRUE);

Datasource Campaigns have a field "trunk" defined as:

    DataSourceField fTrunk  = new DataSourceField(
   开发者_开发百科         "trunk",
            FieldType.INTENUM,
            "Trunk"
    );
    fTrunk.setMultiple(Boolean.TRUE);
    fTrunk.setForeignKey("CfgTrunkDS.trunkId");

And here is the form definition to allow for multiple values being selected:

    final DynamicForm form = new DynamicForm();
    form.setIsGroup(true);
    form.setGroupTitle("Update Campaign");
    form.setNumCols(4);

    form.setDataSource(dsCampaign);
    form.setUseAllDataSourceFields(Boolean.TRUE);

    final SelectItem selectItemMultipleGrid = new SelectItem("trunk");
    selectItemMultipleGrid.setTitle("Trunk to use");
    selectItemMultipleGrid.setMultiple(true);
    selectItemMultipleGrid.setMultipleAppearance(MultipleAppearance.PICKLIST);
    selectItemMultipleGrid.setOptionDataSource(CfgTrunkDS.getInstance());
    selectItemMultipleGrid.setValueField("trunkId");
    selectItemMultipleGrid.setDisplayField("trunkName");


    form.setFields(selectItemMultipleGrid);

I also see the multiple values correctly and if I look at the "trunk" fiels, I see a string like "12, 16" when I select elements whose ids are 12 and 16. But still does not pass validation. I also noticed that if I comment the OptionDataSource in the form definition, it works just as fine.

What did I do wrong?

if(selectItemMultipleGrid.getValueASString ==  null){  
    SC.say("Please Select MultipleItem");  
}