Unable to put null values in JSON object

According to RFC 4627, JSON treats the null symbol as a valid value.

The catch is that JSON null is the representation for the Javascript null value. By contrast, the Java version of null is (according to the experts) more closely aligned with Javascript's undefined value.

The original author of the org.json library decided that JSONObject should treat JSON null in a way that is consistent with the Javascript semantics. Hence it is represented (in Java) as JSONObject.NULL ... which is not equal to null.

Right there in the documentation, in the first paragraph:

Values may not be null, NaNs, infinities, or of any type not listed here.

So yes, it is "...something that null values are not included..." (edit: that was a quote from your original question; your updated question changes it to "uninitialized values" but the default value of an object reference is null, so...)

It's a "feature" of that class, though; JSON itself understands null just fine. Further down in the documentation it says you use a "sentinal value," NULL, to represent null. Which seems...odd. There's a note about it:

Warning: this class represents null in two incompatible ways: the standard Java null reference, and the sentinel value NULL. In particular, calling put(name, null) removes the named entry from the object but put(name, JSONObject.NULL) stores an entry whose value is JSONObject.NULL.

So:

params.put(KEY_TOKEN, token == null ? JSONObject.NULL : token);

I solved this by creating a class that extends JSONObject and overriding the method put to use JSONObject.NULL when the passed object is null

public class ObjectJSON extends JSONObject {
    public JSONObject put(String key, Object value) throws JSONException {
        return super.put(key, value == null ? JSONObject.NULL : value);
    }
}