help with javax.jcr.NamespaceException (Unknown namespace URI). Thanks!

This is very simple servlet and just to test I was trying to understand issue with adaptTo here -

package com.aem.demo.core.servlets;

import java.io.IOException;

import javax.jcr.RepositoryException;
import javax.servlet.Servlet;

import org.apache.sling.api.SlingHttpServletRequest;
import org.apache.sling.api.SlingHttpServletResponse;
import org.apache.sling.api.resource.ResourceResolver;
import org.apache.sling.api.servlets.HttpConstants;
import org.apache.sling.api.servlets.SlingAllMethodsServlet;
import org.osgi.service.component.annotations.Component;

import com.adobe.granite.security.user.UserProperties;

@8220494(service = Servlet.class, property = { "sling.servlet.paths=" + "/bin/username",
"sling.servlet.methods=" + HttpConstants.METHOD_GET })
public class UserPropertiesServlet extends SlingAllMethodsServlet {




/**
*
*/
private static final long serialVersionUID = -3561858749807565841L;

protected void doGet(SlingHttpServletRequest slingHttpServletRequest, SlingHttpServletResponse slingHttpServletResponse) {

ResourceResolver resourceResolver = slingHttpServletRequest.getResourceResolver();

UserProperties userProperties = resourceResolver.adaptTo(UserProperties.class);
try {
slingHttpServletResponse.getWriter().write(userProperties.getDisplayName());
} catch (IOException | RepositoryException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

But I didn't face such problem and here is the servlet response -

Could you please tell me what are you trying to achieve via the servlet or code overview.