fix read error when sdo_geometry is empty.

[nocny-x]

When geometry parameter is null, OraWriter.write() will create an empty geometry(ordDim=0) to store, then OraReader.read() will throw an error, I think it should return null when it is empty.

[dr-jts]

Should have a unit test that covers this case. Also Javadoc.

[dr-jts]

In general JTS operations usually return an empty GeometryCollection to indicate empty results. This means that chained geometry operations continue to work. Perhaps that is a better pattern to use here?

Do ordDim=0 Oracle geometrys ever occur in real life? If so, what do they represent?