Using reflection to invoke Type parameterized methods

The google cloud dataflow sdk has a class that registers Coders for different Avro types.

CoderRegistry cr = p.getCoderRegistry();
cr.registerStandardCoders();
cr.registerCoder(Row.class, AvroCoder.of(Row.class));
cr.registerCoder(Destination.class, AvroCoder.of(Destination.class));
cr.registerCoder(Device.class, AvroCoder.of(Device.class));
cr.registerCoder(Location.class, AvroCoder.of(Location.class));
cr.registerCoder(Source.class, AvroCoder.of(Source.class));
cr.registerCoder(DimensionalMetric.class, AvroCoder.of(DimensionalMetric.class));
cr.registerCoder(DimensionSet.class, AvroCoder.of(DimensionSet.class));
cr.registerCoder(MetricSet.class, AvroCoder.of(MetricSet.class));

But as you can imagine this gets pretty cumbersome and I would like to use java reflection API to automatically register all classes in the package com.brightcove.rna.model. I imagine this would look something like this:

void registerAllModels(Pipeline p) {
    CoderRegistry cr = p.getCoderRegistry();
    Reflections r = new Reflections("com.brightcove.rna.model");
    Set<Class<? extends IndexedRecord>> classes = r.getSubTypesOf(IndexedRecord.class);
    for (Class<? extends IndexedRecord> clazz : classes) {
        cr.registerCoder(clazz, AvroCoder.of(clazz));
    }
}

Unfortunately, this doesn't work. What am I doing wrong here?