private void makeAttributeTransformIfAppropriate(SummaryField summaryField, Schema schema) {
        if (summaryField.getTransform() != SummaryTransform.NONE) return;
        Attribute attribute = schema.getAttribute(summaryField.getSingleSource());
        if (attribute == null) return;
        summaryField.setTransform(SummaryTransform.ATTRIBUTE);
    }
If the source is an attribute, make this use the attribute transform
config-model/src/main/java/com/yahoo/schema/processing/AdjustSummaryTransforms.java