public Builder<K, V> addField(K name, V value) {
            Objects.requireNonNull(name, "name");
            final V duplicateKey = node.put(name, value);
            if (throwIfDuplicateKeys) {
                if (duplicateKey != null) {
                    throw new IllegalArgumentException("Duplicate key: " + name);
                }
            }
            return this;
        }
@param nameMapper nameMapper does not guarantee uniqueness.
commons-server/src/main/java/com/navercorp/pinpoint/common/server/util/json/JsonFields.java