@Override
    public SDField getConcreteField(String name) {
        SDField field = getExtraField(name);
        if (field != null) return field;

        return (SDField) documentType.getField(name);
    }
Returns a field defined in this search definition or one if its documents. Fields in this search definition takes
precedence over document fields having the same name

@param name of the field
@return the SDField representing the field
config-model/src/main/java/com/yahoo/schema/Schema.java