jodd-json/src/main/java/jodd/json/JsonObject.java
public JsonObject putNull(final String key) {
		Objects.requireNonNull(key);
		map.put(key, null);
		return this;
	}
public JsonObject putNull(final String key) {
		Objects.requireNonNull(key);
		map.put(key, null);
		return this;
	}
Puts a {@code null} value into the JSON object with the specified key.