title: Getting null pointer exception while running helloworld in drools
body: <p>I got the following error while running a simple helloworld sample drools project.</p>
  
  <pre><code>199 [main] ERROR org.drools.compiler.kie.builder.impl.KieContainerImpl - Unknown KieSession name: ksession-rules
  java.lang.NullPointerException
      at com.sample.DroolsTest.main(DroolsTest.java:24)
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>package com.sample;
  
  import org.kie.api.KieServices; import
  org.kie.api.runtime.KieContainer; import
  org.kie.api.runtime.KieSession;
  
  /**  * This is a sample class to launch a rule.  */ public class
  DroolsTest {
  
      public static final void main(String[] args) {
          try {
              // load up the knowledge base
              KieServices ks = KieServices.Factory.get();
              KieContainer kContainer = ks.getKieClasspathContainer();
              KieSession kSession = kContainer.newKieSession("ksession-rules");
  
              // go !
              Message message = new Message();
              message.setMessage("Hello World");
              message.setStatus(Message.HELLO);
              kSession.insert(message);
              kSession.fireAllRules();
          } catch (Throwable t) {
              t.printStackTrace();
          }
      }
  
      public static class Message {
  
          public static final int HELLO = 0;
          public static final int GOODBYE = 1;
          private String message;
          private int status;
  
          public String getMessage() {
              return this.message;
          }
  
          public void setMessage(String message) {
              this.message = message;
          }
  
          public int getStatus() {
              return this.status;
          }
  
          public void setStatus(int status) {
              this.status = status;
          }
  
      }
  
  }
  </code></pre>
  
  <p>drools code:</p>
  
  <pre><code>package com.sample
  import com.sample.DroolsTest.Message;
  
  rule "Hello World"
  when
      m : Message( status == Message.HELLO, myMessage : message )
  then
      System.out.println( myMessage );
      m.setMessage( "Goodbye cruel world" );
      m.setStatus( Message.GOODBYE );
      update( m );
  end
  
  rule "GoodBye"
  when
      Message( status == Message.GOODBYE, myMessage : message )
  then
      System.out.println( myMessage );
  end
  </code></pre>