Error when compiling class Foo extends Array

[bcherny]

class Columns extends Array

TypeError: Cannot read property 'freeVariable' of undefined
  at Class.exports.Class.Class.compileNode (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:1600:46)
  at Class.exports.Base.Base.compileToFragments (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:83:21)
  at Return.exports.Return.Return.compileNode (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:659:48)
  at Return.exports.Base.Base.compileToFragments (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:83:21)
  at Return.exports.Return.Return.compileToFragments (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:650:52)
  at Block.exports.Block.Block.compileNode (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:387:28)
  at Block.exports.Block.Block.compileWithDeclarations (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:480:19)
  at Code.exports.Code.Code.compileNode (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:2043:63)
  at Code.exports.Base.Base.compileToFragments (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:83:21)
  at Call.exports.Call.Call.compileNode (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:1025:51)
  at Call.exports.Base.Base.compileToFragments (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:83:21)
  at Block.exports.Block.Block.compileNode (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:387:28)
  at Block.exports.Block.Block.compileWithDeclarations (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:480:19)
  at Block.exports.Block.Block.compileRoot (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:452:24)
  at Block.exports.Block.Block.compileToFragments (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/nodes.js:369:21)
  at Object.<anonymous> (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/coffee-script.js:64:38)
  at Object.compile (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/coffee-script.js:34:19)
  at compileScript (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/command.js:232:33)
  at compilePath (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/command.js:174:14)
  at compilePath (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/command.js:154:22)
  at compilePath (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/command.js:154:22)
  at compilePath (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/command.js:154:22)
  at Object.exports.run (/Users/bcherny/webapp/node_modules/coffee-script/lib/coffee-script/command.js:98:20)
  at Object.<anonymous> (/Users/bcherny/webapp/node_modules/coffee-script/bin/coffee:7:41)
  at Module._compile (module.js:435:26)
  at Object.Module._extensions..js (module.js:442:10)
  at Module.load (module.js:356:32)
  at Function.Module._load (module.js:313:12)
  at Function.Module.runMain (module.js:467:10)
  at startup (node.js:136:18)
  at node.js:963:3