optJSONObject() add default value

[tilds]

I found myself often needing a version of optJSONObject where I could define my own default value as the 2nd argument (as you can on most of the other 'opt' methods).

The use case is when I need to access something that is nested deep in a json object, I currently have to check for null for every level of nesting, but if I could just set the default value to be and empty jsonobject instead of null, I could do something like this:
String nestedvalue = jsonObject.optJSONObject("key", new JSONObject()).optJSONObject("key", new JSONObject()).optJSONObject("key", new JSONObject()).optString("nestedvalue")

Let me know what you think :)

[johnjaylward]

Looks good to me. Thanks for the contribution.

[stleary]

What problem does this code solve?
One of the opt() functions does not have a default return value param

Risks
Low

Changes to the API?
Adding a new API method

Will this require a new release?
No

Should the documentation be updated?
No, but the JavaDocs will be slightly out of date

Does it break the unit tests?
No, but some unit tests were repurposed. The originals will be restored later.

Was any code refactored in this commit?
No

Review status
APPROVED
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