private void assertEqualTransform(SummaryField field1, SummaryField field2) {
        if ( ! field2.getTransform().equals(field1.getTransform())) {
            throw new IllegalArgumentException("Conflicting summary transforms. " + field2.toLocateString() +
                                               " is already defined as " +
                                               field1.toLocateString() + ". A field with the same name " +
                                               "can not have different transforms in different summary classes");
        }
    }
Ensure that summary field transforms for fields having the same name
are consistent across summary classes

@author bratseth
config-model/src/main/java/com/yahoo/schema/processing/SummaryConsistency.java