setShowGridSummary throws Invocation Exception

Question

maybe someone can help me. I'm in trouble with SmartGWT method "setShowGridSummary", when I try to set this property this method throws Invocation Exception.

my code looks like this:

 private void parseSummaryData(ArrayList<LinkedHashMap<String, String>> summaryMetaData) {
    ListGridField[] listGridFields = cachedFields;

    ClientSummaryData clientSummaryData = new ClientSummaryData();

    for (ListGridField listGridField : listGridFields) {
        String gridName = listGridField.getName();
        for (LinkedHashMap<String, String> column : summaryMetaData) {
            String columnName = column.get("columnName");
            if (columnName.equals(gridName)) {
                if (column.containsKey("setValue")) {  
                    listGridField.setShowGridSummary(true);
                    listGridField.setSummaryValue(column.get("setValue"));
                    clientSummaryData.setShowGridSummary(true);
                    clientSummaryData.setNoAggregating(false);
                } else {
                    clientSummaryData = parseClientSummaries(column, listGridField, clientSummaryData);
                }
            }
        }
    }
    this.setShowGridSummary(clientSummaryData.isShowGridSummary());
    this.setShowGroupSummary(clientSummaryData.isShowGroupSummary());
    this.setShowGroupSummaryInHeader(clientSummaryData.isShowGroupSummaryInHeader());
}

and one more thing - I manage to find this JavaScriptException when all this happening: this.sourceWidget.completeFields is undefined