Schema XSD restriction

[[email protected]]

Is it possible to write and element restrictions such that "" or null is an acceptable value?

E.g., can the following be adapted so than a "" or null value is also acceptable?

<xs:element name="age">
<xs:simpleType>
<xs:restriction base="xs:integer">
<xs:minInclusive value="0"/>
<xs:maxInclusive value="120"/>
</xs:restriction>
</xs:simpleType>
</xs:element>

Thank you.