@Override
 public void setReturnType(Class<?> returnType) {
   if (returnType == null) {
     throw new IllegalArgumentException("Return type cannot be null.");
   }
   outline.setReturnType(JavaType.from(returnType));
 }
  @Override
  public void setReturnType(String returnType) {
    if (returnType == null) {
      throw new IllegalArgumentException("Return type cannot be null.");
    }

    final JavaType type;
    try {
      type = JavaType.from(returnType);
    } catch (ParseException e) {
      throw new DescriptorBuilderException("invalid return type '" + returnType + "'");
    }

    outline.setReturnType(type);
  }