cannot add row to datatable primefaces 5.0 - jsf

Question

I read many answers abot this issue, they say I should add an item to the list that feed the datatable and then refresh the form, but this does not work in my progect. this is my datatable:
<p:dataTable var="rowItem"
scrollable="true"
scrollHeight="100%"
id="flussiGuestSummary"
emptyMessage="nessun flusso guest selezionato"
value="#{fileMatchMB.selectedGuests}"
rowKey="#{rowItem.row}">
style="width:10px;text-align:center" />
<p:column headerText="Date Valuta"
width="30">
<h:outputText value="#{rowItem.data}">
<f:converter
converterId="filematch.interfaccia.CalendarConverter" />
</h:outputText>
</p:column>
<p:column headerText="Importo"
style="text-align: center; width:30px;">
<h:outputText value="#{rowItem.amount}">
<o:converter converterId="javax.faces.Number"
currencySymbol="#{rowItem.getCurrencySymbol()}"
type="currency" />
</h:outputText>
</p:column>
<p:column headerText="Descrizione"
styleClass="scrollableCell"
style="text-align: center; width:80px;">
<h:outputText value=" #{rowItem.descrizione}">
<f:converter converterId="filematch.interfaccia.StringShortner" />
<f:attribute name="shortnerActive"
value="#{fileMatchMB.shortnerActive}" />
</h:outputText>
</p:column>
<p:column headerText="Causale"
styleClass="scrollableCell"
style="text-align: center; width:30px;">
<h:outputText value=" #{rowItem.causale}"
width="100">
<f:converter converterId="filematch.interfaccia.StringShortner" />
<f:attribute name="shortnerActive"
value="#{fileMatchMB.shortnerActive}" />
</h:outputText>
</p:column>
<p:column headerText="match"
styleClass="scrollableCell"
style="text-align: center; width:10px;">
<h:outputText value=" #{rowItem.match}">
<f:converter converterId="filematch.interfaccia.StringShortner" />
<f:attribute name="shortnerActive"
value="#{fileMatchMB.shortnerActive}" />
</h:outputText>
</p:column>
<f:facet name="footer">
"#{fileMatchMB.countGuest} / #{fileMatchMB.guestList.size()} #{msg.msg_records}"
</f:facet>
</p:dataTable>
the code in the backing bean:
this.selectedGuests = selected_list;
I am sure selected_list is nort empty, but my datatable remains empty, what am I doing wrong?