if( ruleExpression.getContractedMatchExpression() != null )
{
if( contractedTransformer == null )
throw new IllegalArgumentException( "must have contracted expression if given contracted match expression" );
subGraphTransformer = new SubGraphTransformer( contractedTransformer, ruleExpression.getContractedMatchExpression() );
}
else
{
subGraphTransformer = null;
}