How to ignore some field with dapper

I have a "Product" api like this:

public Task<int> UpdateProduct(ProductRequest request)
{......}
public class ProductRequest 
{
    public int Id{get;set;}
    public string Code{get;set;}
    public string Name{get;set;}
    public string Brand{get;set;}
    ...... 
}

the client sometimes want to update the name only. so the argument like this { Id:123, Name:"newName"}, But the argument received by the server becomes :

public class ProductRequest 
{
   public int Id   //123
   public string Code   //null
   public string Name   //"newName"
   public string Brand //null
   ...... 
}

// use sqlbuilder to generate sql text.
// etc.....

As you see, The server can't tell what needs to be updated, unless the fields has some value. the other null fields were confused, maby the client want to update it to NULL, or ignore it.
I don't want to seach it from database first and edit it and save it .. i think the search is redundant.

What should I do in this case?

No source file, test, or entry point is identified; begin by locating the ProductRequest handling and SQL-builder usage in the repository. Clarify how the update should distinguish omitted fields from explicit NULL values, then define tests showing both cases and the expected generated SQL before considering the work complete.