code: public Object call(Closure c) throws IOException {
          writer.write("{");
          StreamingJsonDelegate.cloneDelegateAndGetContent(writer, c);
          writer.write("}");
  
          return null;
      }
docs: A closure passed to a JSON builder will create a root JSON object
  <p>
  Example:
  <pre class="groovyTestCase">
  new StringWriter().with { w ->
  def json = new groovy.json.StreamingJsonBuilder(w)
  json {
  name "Tim"
  age 39
  }
  
  assert w.toString() == '{"name":"Tim","age":39}'
  }
  </pre>
  
  @param c a closure whose method call statements represent key / values of a JSON object