Handle nulls in fixture tables using setNull to fix Teradata failures

This change fixes some of the `null` handing issues with the Teradata adapter.

This also allows us to use the `CoreTests` suite as there are no `null` parameters (set via `Set Parameter`) used.

Partially resolves #318.

That should be on same line as if's closing brace: http://web.archive.org/web/20090806170521/http://java.sun.com/docs/codeconv/html/CodeConventions.doc6.html#449