public Attribute addAttribute(Attribute attribute) {
        String name = attribute.getName();
        if (name == null || name.isEmpty()) {
            name = getName();
            attribute.setName(name);
        }
        attributes.put(attribute.getName(),attribute);
        return attribute;
    }
Returns the search-time attribute settings of this field or null if none is set.
config-model/src/main/java/com/yahoo/schema/document/SDField.java