JSF :: Passing Argument Parameters Between Pages

So I have an application where the user logs in (using j_security_check). User is taken to a welcome page where user's name is displayed as a link. When clicking that link I would like to take the user to a page where the user is able to update the credentials (password, address, etc). In this way the user only has access to the link related to that specific user's credentials. I am trying the following structure:

The welcome page (adminindex.xhtml) is:

<h:form>
Welcome to admin <h:commandLink value="#{userb.loggedUser}" action="#{userb.selectedUser}"/>
<f:param name="userName" value="#{userb.userName}"/>
</h:form>

The user backing bean:

public String selectedUser() {
userName = FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap().get(userName);
selUser=uServ.findByName(userName);
return "UpdateUser";

[Code] ....

The last line of the stack suggests that a null PK value is being picked up by the FacesContext method in the backing bean. I'm confused because the userName string IS the primary key of the user table which is structured like this:

CREATE TABLE sha_users
( username VARCHAR(255) NOT NULL
, password VARCHAR(255) NULL
, PRIMARY KEY ( username ) );

I'm sure I'm getting the concept of how to pass query parameters...