@Test
public void testAsStringNullValues() {

    PortableBooleanParameterDefinition p1 = new PortableBooleanParameterDefinition();
    assertEquals( "null",
                  p1.asString() );
    PortableEnumParameterDefinition p2 = new PortableEnumParameterDefinition();
    p2.setClassName( "Smurf" );
    assertEquals( "null",
                  p2.asString() );
    PortableFloatParameterDefinition p3 = new PortableFloatParameterDefinition();
    assertEquals( "null",
                  p3.asString() );
    PortableIntegerParameterDefinition p4 = new PortableIntegerParameterDefinition();
    assertEquals( "null",
                  p4.asString() );
    PortableObjectParameterDefinition p5 = new PortableObjectParameterDefinition();
    assertEquals( "null",
                  p5.asString() );
    PortableStringParameterDefinition p6 = new PortableStringParameterDefinition();
    assertEquals( "null",
                  p6.asString() );
}