c# - Sending an update statement to sql-server using Dapper without all properties having values -

i have simple update function in data access layer uses dapper , updates product.

public static void updateproduct(product product) {   using (var connection = getopenconnection())   {     stringbuilder updatesql = new stringbuilder();     updatesql.appendline("update proformaassumption ");     updatesql.appendline("set categoryid = @categoryid ");     updatesql.appendline("   ,purchasedate = @purchasedate ");     updatesql.appendline("   ,type = @type ");     updatesql.appendline("where id = @id;");      connection.execute(updatesql.tostring(), product);   } } 

lets have create product scratch in code , want update existing product based on , know existing product's id. want update category, not other fields object not have fields set.

product product = new product(); product.id = 325; product.categoryid = 16; productdal.updateproduct(product); 

i getting 2 errors: purchasedate: error - sqldatetime overflow. must between 1/1/1753 12:00:00 , 12/31/9999 11:59:59 pm
, cannot insert null value type

i need find way tweak update function update items values. have wrap if statement around each appendline like:

if (product.type != null)  {   updatesql.appendline("   ,type = @type "); } 

i not sure if problem dapper related or sending values sql c# in general. thought dapper made things easy.