public SummaryField getSummaryField(String name, boolean create) {
        SummaryField summaryField = summaryFields.get(name);
        if (summaryField == null && create) {
            summaryField = new SummaryField(name, getDataType(), this);
            addSummaryField(summaryField);
        }
        return summaryFields.get(name);
    }
Returns a summary field defined (implicitly or explicitly) by this field.

@param create true to create the summary field and add it to this field before returning if it is missing
@return the summary field, or null if not present and create is false
config-model/src/main/java/com/yahoo/schema/document/SDField.java