I want to display all invoices that doesn't have a PaymentDate

[#1]

Hi

I have to tables

One named invoice that displays invoice information. I want to display all invoices that doesn't have a PaymentDate and I cant get it right. I tried NULLASVALUE  any tips? Because PaymentDate only exist after payment the value dose therefore not exist, so how can I find it, and null as value does not seem to work

LOAD
Pid,
IKey,
"Place_ID"
IDate
IAmount,
Status;
SQL SELECT *
FROM "Test".dbo.Invoice
WHERE InvoiceAmount >=1;

LOAD
IKey,
"Payments_ID",
"AccountDetail_ID",
PaymentDate,
PaymentAmount,
PrositStatus;
SQL SELECT *
FROM "Test".dbo.Invoice

thx Theo

[#2]

Thank you for your answer but the problem is fixed now. I didn't have a chance to test all the solutions but the solution from Mark did the trick.

Thank you for your answer

Theo