Define nillable element with content type which requires content. Try nillable=false.
http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/#cElement_Declarations
TEST nillable00101m2 - nillable=false (negative case) (valid schema)
| Item | Value | 
|---|---|
| title | nillable00101m2 - nillable=false (negative case) (valid schema) | 
| name | nillable00101m2 | 
| source | ../nillable00101m2.xsd | 
| schemaName | ../nillable00101m2.xsd | 
| executeClass | com.sun.jaxb_tck.sigtest.JAXBTest | 
| executeArgs | -TestURL $testURL -Plugin com.sun.jaxb_tck.sigtest.JaxbPlugin -FileName nillable00101m2.sig -PackageWithoutSubpackages $package | 
| keywords | schema positive | 
| package | javasoft.sqe.tests.elemdecl.nillable.nillable00101m.nillable00101m2 | 
| signature | nillable00101m2.sig |