All content types are an extension of the moduleNodeMigration class, which is itself an extension of the abstract class DrupalNode6Migration. At the beginning of each class, you must include a constructor with an $arguments array as follows:

class hr_migrateTypeMigration extends hr_migrateNodeMigration {
  public function __construct(array $arguments) {

All custom field mappings go inside the constructor, and any extra functions for the class will go inside the class, but outside the constructor.