Attempting to json-encode a Twitter::NullObject with ActiveSupport results in SystemStackError

[lukevmorris]

Right after we upgraded to Rails 4.1, we started noticing periodic SystemStackErrors being raised by our application when performing and rendering results from Twitter::REST::Client#search. This appears to be caused by an interaction between Twitter::NullObject and ActiveSupport::JSON::Encoding::JSONGemEncoder#jsonify, where:

null_attr = Twitter::NullObject.new
ActiveSupport::JSON.encode(null_attr)

results in an infinite loop:

ActiveSupport::JSON::Encoding::JSONGemEncoder:79 - jsonify
Twitter::NullObject::GeneratedMethods:90 - method_missing
Twitter::NullObject::GeneratedMethods:27 - method_missing
ActiveSupport::JSON::Encoding::JSONGemEncoder:79 - jsonify
Twitter::NullObject::GeneratedMethods:90 - method_missing
Twitter::NullObject::GeneratedMethods:27 - method_missing
...

and eventually:

SystemStackError: stack level too deep

This pull request gives Twitter::NullObject the knowledge that its json representation is 'null', and thereby allows #jsonify to exit its infinite recursion. This seems to me to be a reasonable addition to NullObject's responsibilities, though I can definitely see an argument that it shouldn't be concerned at all with json encoding. Let me know what you think and whether there are any additional changes you'd like me to make.

[sferik]

I’m okay with this. Thanks for the patch. I’ll merge it into the master branch, which is tracking the next major release (a.k.a. v6). If necessary, I can also backport it into the 5-stable branch and push a bugfix release (5.14.1). Let me know what your needs are.

[lukevmorris]

Thanks @sferik. A backport would be very convenient if v6 is still a ways off.

[sferik]

@lukevmorris There are still lots of open issues for v6, so I’ll backport your changes now. I’m not going to ship a new gem right away but ping me again when you need that.

[sferik]

@lukevmorris Okay, I’ve cherry-picked your change into the 5-stable branch: 0f8bd7e.