Save and update on same xhtml is not working in primefaces - jsf-2

Question

Hi i tried the following functionality using primefaces.
In my xhtml i have a input field which takes input and saves into db.After completion of save i display the saved data in data table of primefaces.
Upto now works fine.now i add single selection to datatable .when user click on the row i update the same input column with selected data.
For this i use the following code
<h:form id="form">
<p:growl id="messages" />
<p:panel id="panel" header="Currency">
<h:panelGrid columns="2" id="currencyGrid">
<p:outputLabel value="Currency :"/>
<p:inputText value="#{currencyBean.currencyMaster.currDesc}"/>
</h:panelGrid>
<p:commandButton value="Add" action="#{currencyBean.saveCurrency}"
update="currencytable">
</p:commandButton>
<p:dataTable id="currencytable" var="cur"
value="#{currencyBean.currencyList}" widgetVar="dlg"
selection="#{currencyBean.currencyMaster}"
selectionMode="single" rowKey="#{cur.currId}">
<p:ajax event="rowSelect" listener="#{currencyBean.onRowSelect}"
update=":form:currencyGrid" />
<p:column headerText="ID" style="font-size:12px;">
<h:outputText value="#{cur.currId}" />
</p:column>
<p:column headerText="Description" style="font-size:12px;">
<h:outputText value="#{cur.currDesc}" />
</p:column>
</p:dataTable>
</h:form>
And My Bean code is:
#managedBean
#viewScoped
#component
public class CurrencyBean implements Serializable{
private static final long serialVersionUID = 1L;
#Autowired
private CurrencyMaster currencyMaster;
private List<CurrencyMaster> currencyList;
public CurrencyMaster getCurrencyMaster() {
return currencyMaster;
}
public void setCurrencyMaster(CurrencyMaster currencyMaster) {
this.currencyMaster = currencyMaster;
}
public void saveCurrency(){
try{
currencyService.saveCurrency(currencyMaster);
}catch(Exception e){
e.printStackTrace();
}
}
#PostConstruct
public void currencyList(){
setCurrencyList(currencyService.getCurrencyList());
}
public void onRowSelect(SelectEvent event) {}
public void onRowUnselect(UnselectEvent event) {}
}
So when i click on currrencytable row the input field populated properly and update operation also.
The problem is when i directly enter the data into input column my globalMaster property is going to be null.
And the following error is occured;
attempt to create saveOrUpdate event with null entity
I change the scopes of the bean but i did not find the solution.
And i find more solutions for the above exception but my problem is the new values are does not set to currencymaster.
Is there any mistake i done in this context.please guide me..