DIALOG:
====================================
<p:dialog
        header="New Person"
        widgetVar="newPersonDialog"
        resizable="false" modal="true"
        closeListener="#{newPersonBean.handleDialogClose}">

        <h:form id="newPersonForm">
            <h:panelGrid columns="2">
                <h:outputText value="First name" />
                <h:panelGroup>
                    <p:inputText value="#{newPersonBean.person.firstName}" id="firstname" size="30" required="true">
                        <f:validateLength maximum="45"/>
                    </p:inputText>
                    <br/>
                    <h:message for="firstname" />
                </h:panelGroup>

                <h:outputText value="Other value" />
                <p:inputText value="#{newPersonBean.person.value}" required="false" />
            </h:panelGrid>

            <!-- Is empty after updating the form and reopening the dialog while the inputText with the same value is not empty -->
            <h:outputText value="#{newPersonBean.person.value}" />

            <p:commandButton value="Save"
                actionListener="#{newPersonBean.processPerson}"
                update="@form notifications"
                oncomplete="handleNewPersonDialogClose(xhr, status, args)"
            />
        </h:form>
</p:dialog>


COMMANDBUTTON
====================================
<p:commandButton
    value="New person"
    oncomplete="newPersonDialog.show();"
    update="newPersonForm"
/>