Unable to add a Vector Store to a new Assistant thread.

[joycpa]

Am trying to add a vector store to a new Assistant thread. Have added the vectorStore.Id to the fileSearchToolResources and then included it in the ThreadCreationOptions. Following is the code. Am getting a null reference error.

//Add vector store to thread
FileSearchToolResources fileSearchToolResources = new FileSearchToolResources();
fileSearchToolResources.NewVectorStores.Clear();
fileSearchToolResources.VectorStoreIds.Add(vectorStore.Id);

ThreadRun threadRun;
try
{

ThreadCreationOptions threadOptions = new()
{ 
    ToolResources =
    {
        FileSearch = fileSearchToolResources,
    },


    InitialMessages = { "New file uploaded " + FileUploaded.Id + " Create Profit and Loss Statement from this uploaded file. " }

};

threadRun = assistantClient.CreateThreadAndRun(_globalSettings.AssistantId, threadOptions);

}