Select against a "null" condition

[#1]

Hello.  I'm a newbie in QlikView, and need a little help:

I have the following table:

ID_Workflow  Phase  Task  Asigned

1001         01     null    Carl

1001         01     01      John

1001         01     02      Samantha

I need to do the equivalent to "SELECT * FROM <table> WHERE Task is NULL"

What is the equivalent syntax in QlikView?  I need to do in the load script, or I can do it in a Chart ?

Thank you!

[#2]

I want to thank to everyone that answer this post. 

I used the switch "NullAsValue" / "NullAsNull",  as Bill show in the last post.  However, all of your answers was very helpfull for me; to understand how works QlikView.

Anders, Fernando, Matthieu, Ralf, Mayil, Amuthabharathi, Matthew, Bill: Thank you!!!!

[#3]

I do something like this:

LOAD

  If(Len([Field1]) = 0, 0, [Field1]) as [Field1],

  If(Len([Field2]) = 0, 0, [Field2]) as [Field2],

  If(Len([Field3]) = 0, 0, [Field3]) as [Field3]

FROM

QVDs\myfile.qvd (qvd);

[#4]

Hi,

Matthieu thank you very much i will use it in future

Thanks and regards,

S.Amuthabharathi