if ( args.size() != 0 ) {
String[] a = args.get( 0 );
String name = a[0].trim();
String leftInput = a[1].trim();
LeftTupleSource leftTupleSource;
if ( "mock".equals( leftInput ) ) {
leftTupleSource = new MockTupleSource( buildContext.getNextId() );
} else {
leftTupleSource = (LeftTupleSource) context.get( leftInput );
}