public void addStructField(ParsedField structField) {
        String fieldName = structField.name();
        verifyThat(! structFields.containsKey(fieldName), "already has struct-field", fieldName);
        structFields.put(fieldName, structField);
    }
get an existing summary field for modification, or create it
config-model/src/main/java/com/yahoo/schema/parser/ParsedField.java