code: @SuppressWarnings({ "rawtypes", "unchecked" })
      private AttributeValue getCustomerMarshallerAttributeValue(Method getter, Object getterReturnResult) {
          DynamoDBMarshalling annotation = getter.getAnnotation(DynamoDBMarshalling.class);
          Class<? extends DynamoDBMarshaller<? extends Object>> marshallerClass = annotation.marshallerClass();
  
          DynamoDBMarshaller marshaller;
          try {
              marshaller = marshallerClass.newInstance();
          } catch ( InstantiationException e ) {
              throw new DynamoDBMappingException("Failed to instantiate custom marshaller for class " + marshallerClass,
                      e);
          } catch ( IllegalAccessException e ) {
              throw new DynamoDBMappingException("Failed to instantiate custom marshaller for class " + marshallerClass,
                      e);
          }
          String stringValue = marshaller.marshall(getterReturnResult);
  
          return new AttributeValue().withS(stringValue);
      }
docs: Returns an attribute value for the getter method with a custom marshaller