Problem about Command object in dataenvironment...(編號:3040)

How to use a command to add a record with null field into access DB ??
I create a INSERT command with some parameters, but I cannot use the following statement ( it raises a error)
DataEnvironment1.Command1 name, age,,, 20
(I want to set the 4th and 5th parameters to be NULL value ...)
can anyone teach me how to do it?