Bug: Custom data parts break subsequent messages with Gemini

Unable to submit request because it must include at least one parts field, which describes the prompt input. Learn more: https://cloud.google.com/vertex-ai/generative-ai/docs/model-reference/gemini

execute: async (inputData, { writer }) => {
  await writer?.custom({
    type: "data-chart",
    data: inputData,
  });
  
  return { success: true };
}