title: Error during get Flavor list: java.lang.NullPointerException: URI template of the newly created target must not be null
body: <p>I am using JSF to develop web application and also using OpenStack4J to work with OpenStack,
  In my bean component I have method:</p>
  
  <pre><code>public List&lt;SelectItem&gt; getFlavorList() {
  
           List&lt;SelectItem&gt; items = new ArrayList&lt;SelectItem&gt;();
  
           OSClient osClient = OSFactory.builder().endpoint("http://xxx.xxx.xxx.xxx:5000/v2.0")
              .credentials("admin", "nova").tenantName("admin").authenticate();
  
           List&lt;? extends Flavor&gt; flavors = osClient.compute().flavors().list();
  
           SelectItem item = null;
           for (Flavor flv: flavors){
                item = new SelectItem();
                item.setLabel(flv.getName());
                item.setValue(flv.getId());
           }
           items.add(item);
  
           return items;
      }
  </code></pre>
  
  <p>If i create a main test to test this method, everything ok, I can get the flavor list from OpenStack, but when i try to call from JSF page it appear a problem.</p>
  
  <p>In My JSF page, I trying to call </p>
  
  <pre><code>            &lt;h:selectOneMenu value="#{dropletBean.droplet.flavorID}"&gt;
                 &lt;f:selectItem itemLabel="Please select one size" /&gt; 
                 &lt;f:selectItems value="#{flavorBean.getFlavorList()}" /&gt;
              &lt;/h:selectOneMenu&gt;
  </code></pre>
  
  <p>The error appear as below. Please help me to check it.</p>
  
  <pre><code>java.lang.NullPointerException: URI template of the newly created target must not be null.
  at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:229)
  at org.glassfish.jersey.client.JerseyClient.target(JerseyClient.java:179)
  at org.glassfish.jersey.client.JerseyClient.target(JerseyClient.java:69)
  at org.openstack4j.core.transport.internal.HttpExecutor.invoke(HttpExecutor.java:73)
  at org.openstack4j.core.transport.internal.HttpExecutor.execute(HttpExecutor.java:52)
  at org.openstack4j.core.transport.internal.HttpExecutor.execute(HttpExecutor.java:43)
  at org.openstack4j.openstack.internal.BaseOpenStackService$Invocation.execute(BaseOpenStackService.java:136)
  at org.openstack4j.openstack.internal.BaseOpenStackService$Invocation.execute(BaseOpenStackService.java:131)
  at org.openstack4j.openstack.compute.internal.FlavorServiceImpl.list(FlavorServiceImpl.java:24)
  at com.vdco.icloud.openstack.web.service.impl.FlavorServiceImpl.getFlavorIDList(FlavorServiceImpl.java:39)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  </code></pre>
  
  <p>Thanks you so much</p>