Errors when using `printAst` and other helper methods related to parsed ASTs

In versions 0.9.0 and up, I can't successfully call any of the AST helper methods.

> var ast = require('lively.ast')
undefined
> ast.printAst(ast.parse("1 + 2"))
TypeError: Cannot read property 'string' of undefined
    at Object.printAst (<yadda\yadda>\node_modules\lively.ast\dist\lively.ast.js:12910:23)
    at repl:1:5
    at sigintHandlersWrap (vm.js:32:31)
    at sigintHandlersWrap (vm.js:96:12)
    at ContextifyScript.Script.runInContext (vm.js:31:12)
    at REPLServer.defaultEval (repl.js:308:29)
    at bound (domain.js:280:14)
    at REPLServer.runBound [as eval] (domain.js:293:12)
    at REPLServer.<anonymous> (repl.js:489:10)
    at emitOne (events.js:101:20)
>

The code above works fine if I use 0.8.1.

Reproduce the failure with lively.ast 0.9.0 or later using ast.parse("1 + 2") followed by ast.printAst, then inspect dist/lively.ast.js at the reported printAst location. Compare the behavior with version 0.8.1 and check whether the other AST helper methods fail similarly; done means these helpers no longer throw for parsed ASTs.