Riffle and Mahout

[Neil Chaudhuri]

Does anyone have any code to share about how to use Riffle (and Cascading) with 
Mahout? I have a class wrapping a Mahout operation, but I am getting a 
NullPointerException when I add this class to my Cascade. I think the key line 
is this:

11/12/19 14:50:14 INFO flow.Flow: [mahoutVectorizer] atleast one sink does not 
exist

This is despite having a method annotated as follows:

@DependencyOutgoing
    public Path getOutgoing() {
        return outputFilePath;
    }

Any insight is appreciated.

Thanks.