code: public static ConstructorNode getDefaultConstructor(ClassNode classNode) {
          for (ConstructorNode cons : classNode.getDeclaredConstructors()) {
              if (cons.getParameters().length == 0) {
                  return cons;
              }
          }
          return null;
      }
docs: Obtains the default constructor for the given class node.
  
  @param classNode The class node
  @return The default constructor or null if there isn't one