Why am I getting an "internal error", just "Assertion failed" when calling createKeyword

Question

Here is my code.  It is called inside a function running under LrTasks.startAsyncTask.  The calls to "Util.writeLog" confirm that createKeyword is called and never returns.  
  Util.catalog:withWriteAccessDo(
      "CreateKwUnderPerson",
      function()
  Util.writeLog("Calling 'createKeyword()'")
  akw = Util.catalog:createKeyword( name, {}, true, nil, true)
  Util.writeLog("'createKeyword()' returned")
              end
I find it disconcerting that there is no more informative error message.   This seems to me to be an Adobe bug, even though the problem presumably originates from something I'm doing wrong.

Answer 1

Thanks, but yes, I did knew this.   It's all working now.   When I first got your message my first reaction was to reply saying "that's not it—it's not nil"; but then I thought "I should check, it would be better if I could say I'd checked", and five minutes after that it was all cleared up.   A lesson. 
Thanks again.  I did download your debugger (and used parts of the package) but thought that for what I was doing just using a logfile, with tail -F, would be enough.  I'm migrating from Aperture and iPhoto, and thought that at the same time I could try to orgaineze my keywords.   It's been frustrating but enjoyable.
And you said in the first message "given the nature of Lua".   After trying to use Applescript to work with Aperture, Lua is positively luminous.
Thanks again,
Bill MItchell