public void addField(ParsedField field) {
        String fieldName = field.name();
        verifyThat(! fields.containsKey(fieldName), "already has field", fieldName);
        fields.put(fieldName, field);
    }
This class holds the extracted information after parsing a "struct"
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/ParsedStruct.java