public ParsedSummaryField addField(ParsedSummaryField field) {
        String fieldName = field.name();
        verifyThat(! fields.containsKey(fieldName), "already has field", fieldName);
        return fields.put(fieldName, field);
    }
This class holds the extracted information after parsing a
"document-summary" block, using simple data structures as far as
possible.  Do not put advanced logic here!

@author arnej27959
config-model/src/main/java/com/yahoo/schema/parser/ParsedDocumentSummary.java