private void addToDestination(String destinationName, SummaryField summaryField, Schema schema) {
        DocumentSummary destination = schema.getSummariesInThis().get(destinationName);
        if (destination == null) {
            destination = new DocumentSummary(destinationName, schema);
            schema.addSummary(destination);
            destination.add(summaryField);
        }
        else {
            SummaryField existingField= destination.getSummaryField(summaryField.getName());
            SummaryField merged = summaryField.mergeWith(existingField);
            destination.add(merged);
        }
    }
Makes implicitly defined summaries into explicit summaries

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