Payload nonEmptyPayload = null;
final List<TestBucket> bucketsWithoutPayloads = Lists.newArrayList();
for (final TestBucket bucket : buckets) {
final Payload p = bucket.getPayload();
if (p != null) {
if (p.numFieldsDefined() != 1) {
throw new IncompatibleTestMatrixException("Test " + testName + " from " + matrixSource + " has a test bucket payload with multiple types: " + bucket);
}
if (nonEmptyPayload == null) {
nonEmptyPayload = p;
} else if (!nonEmptyPayload.sameType(p)) {