NullPointerException when Serialize Array with Null Item

[cristianobiral]

System.NullPointerException: Attempt to de-reference a null object

Class.XMLSerializer.serialize: line 162, column 1
Class.XMLSerializer.serialize: line 183, column 1
Class.XMLSerializer.serialize: line 165, column 1
Class.XMLSerializer.serialize: line 44, column 1
Class.XMLSerializer.serialize: line 57, column 1