#171 Javascript error with button group

[Alessio Ceroni]

I am having an Exception while using Lobo and Cobra (version 0.98.4) in my code to parse a remote form. The same error can be replicated with the Lobo browser
The form contains two input fields of type "radio" with the same name ("MASS") to create a button group.
The url of the form is "http://www.matrixscience.com//cgi/search_form.pl?FORMVER=1&SEARCH=MIS".
The code causing the exception is at line 469:

...
theForm.MASS[1].checked = false;
theForm.MASS[0].checked = true;
...

The exception is

org.mozilla.javascript.EcmaError: TypeError: Cannot set property "checked" of undefined to "false" (http://www.matrixscience.com//cgi/search_form.pl?FORMVER=1&SEARCH=MIS#448)
at org.mozilla.javascript.ScriptRuntime.constructError(ScriptRuntime.java:3229)
at org.mozilla.javascript.ScriptRuntime.constructError(ScriptRuntime.java:3219)
at org.mozilla.javascript.ScriptRuntime.typeError(ScriptRuntime.java:3235)
at org.mozilla.javascript.ScriptRuntime.typeError3(ScriptRuntime.java:3261)
at org.mozilla.javascript.ScriptRuntime.undefWriteError(ScriptRuntime.java:3283)
at org.mozilla.javascript.ScriptRuntime.setObjectProp(ScriptRuntime.java:1423)
at org.mozilla.javascript.Interpreter.interpretLoop(Interpreter.java:2825)
at script.get_cookies(http://www.matrixscience.com//cgi/search_form.pl?FORMVER=1&SEARCH=MIS:448)
at org.mozilla.javascript.Interpreter.interpret(Interpreter.java:2251)
at org.mozilla.javascript.InterpretedFunction.call(InterpretedFunction.java:161)
...