public void addExtraField(SDField field) {
        if (fields.containsKey(field.getName())) {
            deployLogger.logApplicationPackage(Level.WARNING, "Duplicate field " + field.getName() + " in search definition " + getName());
        } else {
            field.setIsExtraField(true);
            fields.put(field.getName(), field);
        }
    }
Adds an extra field of this search definition not contained in a document

@param field to add to the schemas list of external fields
config-model/src/main/java/com/yahoo/schema/Schema.java