Compare date in a sql query

[access]

I have a query inside a form as below



stSql = "SELECT Customer.CUST_ID, Customer.WEIGHT, Customer.START_DATE, Customer.PROJECT " _
& "FROM Customer WHERE " _
& "(Customer.PROJECT='" & Comboproject & "') AND " _
& "(Customer.WEIGHT = " & Nz(txtWeight, "NULL") & ") AND " _
& "(Customer.START_DATE ='" & Nz(txtStartDate, "") & "') "

I'm facing 2 issues with the above query
1. There can be situations where txtWeight can be null, (WEIGHT field type is NUMBER in table). When there is no data entered in txtWeight, I'm getting error message.
2. Also when data is selected from calendar into txtStartDate, i'm getting "data type mismatch ..." error. Do we need to parse the txtStartDate before assigning to Customer.START_DATE as i have seen some ex giving # before and after the date. But still its not working. Can any one please help me out.

[access]

Well, I have removed quotes for txtStartDate in my query and able to resolve the error as below:

stSql = "SELECT Customer.CUST_ID, Customer.WEIGHT, Customer.START_DATE, Customer.PROJECT " _
& "FROM Customer WHERE " _
& "(Customer.PROJECT='" & Comboproject & "') AND " _
& "(Customer.WEIGHT = " & Nz(txtWeight, "NULL") & ") AND " _
& "(Customer.START_DATE =" & Nz(txtStartDate, "") & ") "

But the query is not returning any record eventhough the entry exists in table.

[access]

I'm able to resolve the date issue as below:

Dim strDate as String
strDate = "#" & txtStartDate & "#"

stSql = "SELECT Customer.CUST_ID, Customer.WEIGHT, Customer.START_DATE, Customer.PROJECT " _
& "FROM Customer WHERE " _
& "(Customer.PROJECT='" & Comboproject & "') AND " _
& "(Customer.WEIGHT = " & Nz(txtWeight, "NULL") & ") AND " _
& "(Customer.START_DATE =" & Nz(txtStartDate, "NULL") & ") "

I'm still left with the weight, how can i accept null fields for Number field types?.