private void addField(DocumentSummary docsum, SummaryField field, boolean validate) {
        if (validate && docsum.getSummaryField(field.getName()) != null) {
            throw new IllegalArgumentException("Summary class '" + docsum.name() + "' uses reserved field name '" +
                                               field.getName() + "'.");
        }
        docsum.add(field);
    }
This processor adds all implicit summary fields to all registered document summaries. If another field has already
been registered with one of the implicit names, this processor will throw an {@link IllegalStateException}.
config-model/src/main/java/com/yahoo/schema/processing/ImplicitSummaryFields.java