Handle get/set methods for null values of non-primitive Java types

In JDBC, the get/set methods for non-primitive types like getString, setTime, etc. use Java nulls to represent SQL NULL values. The Trafodion TMUDF interface should do the same. See, for example, https://docs.oracle.com/javase/7/docs/api/java/sql/ResultSet.html#getTime(java.lang.String).