nillable and minOccurs xsd element attributes

You need to decide whether you are thinking about XML as XML, or whether you are thinking about XML as a way to transmit Java (or other) object from here to there.
In XML, nillable permits the construction as an indicator of an explicit absent value, like an SQL NULL. This is semantically different from just . And both are distinct from nothing at all. So, when looking at XML, you have to distinguish four cases:

some content

For any Java item that inherits from Object, JAXB and other mapping technologies need a way to deal with null values. Nillable is the way to do that. If you forbid nillable on something that can be an object, toolkits will annoyingly use an array to find a way to represent absence.
On the other hand, if you have an array, keep in mind that the array itself is an object, and can be null. So, toolkit has to distinguish a zero-element array from a null.
On the other hand, if you have a primitive type (e.g. int), nillable will lead to problems, since there is no mapping from xsi:nil to a primitive.

http://stackoverflow.com/questions/1903062/nillable-and-minoccurs-xsd-element-attributes