NullReferenceException: Object reference not set to an instance of an object

And again:

I get this error (see title)

in this line of code:

if(inventory.fieldContents_.id != 0 && inventory.fieldContents*.id <= manager.Items.Length){*_

All you need to know is the inventory class :
class inv{
* var fieldContents :field[];*
* var quickContents :field[];*
* var lines :int = 5;*
* var perLine :int = 10;*
* var size :Vector2;*
* var spacing :Vector2;*
}
var inventory :inv;
and the field class:
class field{
* public var id :int;*
* public var amount:int;*
}
In the start function i also have this for being sure that there are enaugh fields:
inventory.fieldContents = new field[inventory.lines * inventory.perLine + inventory.perLine];
inventory.quickContents = new field[inventory.perLine];
manager.hovered = new boolean[inventory.fieldContents.Length];
Although everything works as it shoulds this message is very ennoying. Can somebody help me solving the problem?
(BTW: The Cause is defenetly the fieldContents variable not the manager variable)

Try:

if(inventory.fieldContents <em>!= null && inventory.fieldContents_.id != 0 && inventory.fieldContents*.id <= manager.Items.Length)*_</em>