No Value on field (Null) not displayed in Filter Criteria

No Value on field (Null) not displayed in Filter Criteria

Hi,
 
I have the following criteria on a view:
 
((((Status == "Available" && Retail >= 1) && Image_1.contains("http://www.")) && Quantity >= 0) && Ship_Weight_LBS >= 1) edit
 
and I wanted to add "shipping_price" has some value in the field how could I express this in the above criteria.  I don't want to use the word null but in the above criteria if there is no value in "shipping_price" I do not want that record displayed.
 
Any help would be appreciated and how does the ((('s work?  Is each ( representing something?
 
Thanks in advance, Nicholas