* source builder fails to build a module.
*/
public Displace createModule () throws BuilderException {
List<ModuleBuilder> builders = checkSources ();
Module source = builders.get (SOURCE_CHILD).createModule ();
Module x = builders.get (X_CHILD).createModule ();
Module y = builders.get (Y_CHILD).createModule ();
Module z = builders.get (Z_CHILD).createModule ();
return new Displace (source, x, y, z);
}