public void addFieldSet(ParsedFieldSet fieldSet) {
        String fsName = fieldSet.name();
        verifyThat(! fieldSets.containsKey(fsName), "already has fieldset", fsName);
        fieldSets.put(fsName, fieldSet);
    }
This class holds the extracted information after parsing
one schema (.sd) file, using simple data structures
as far as possible.

Do not put complicated logic here!

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