Core/src/main/java/com/braintreepayments/api/Json.java
public static String optString(JSONObject json, String name, String fallback) {
        if (json.isNull(name)) {
            return fallback;
        } else {
            return json.optString(name, fallback);
        }
    }
public static String optString(JSONObject json, String name, String fallback) {
        if (json.isNull(name)) {
            return fallback;
        } else {
            return json.optString(name, fallback);
        }
    }
Returns the value mapped by name if it exists, coercing it if necessary, or fallback if no such mapping exists.

This is a work around for http://code.google.com/p/android/issues/detail?id=13830 returning "null" if the json
value is null.

@param json
@param name
@param fallback
@return {@link String}