title: `Unable to find class` error in Drools
body: <p>I'm trying to define a very simple function in <code>Drools</code> as below:</p>
  
  <pre><code>import java.util.List;
  
  function int sumLengths(List&lt;String&gt; strings) {
      int counter = 0;
      for (String s : strings)
          counter += s.length();
      return counter;
  }
  </code></pre>
  
  <p>but it gives me error:</p>
  
  <pre><code>Exception in thread "main" java.lang.RuntimeException: [ function sumLengths (line:5):
  Unable to resolve type List&lt;String&gt; while building function. java.lang.ClassNotFoundException: Unable to find class 'List&lt;String&gt;' ]
  </code></pre>
  
  <p>any idea?</p>