code: public Object call(List l) throws IOException {
          writer.write(generator.toJson(l));
  
          return l;
      }
docs: A list of elements as arguments to the JSON builder creates a root JSON array
  <p>
  Example:
  <pre class="groovyTestCase">
  new StringWriter().with { w {@code ->}
  def json = new groovy.json.StreamingJsonBuilder(w)
  def result = json([1, 2, 3])
  
  assert result == [ 1, 2, 3 ]
  assert w.toString() == "[1,2,3]"
  }
  </pre>
  
  @param l a list of values
  @return a list of values