(NS_ERROR_NOT_AVAILABLE) [jsdIStackFrame.isNative]

"John J. Barton" <[email protected]>
Newsgroups gmane.comp.mozilla.devel.jsdebugger
Message-ID <[email protected]>
I wrote:
---
if (frame.isNative) return "(native)";
--
And I got
Component returned failure code: 0x80040111 (NS_ERROR_NOT_AVAILABLE) 
[jsdIStackFrame.isNative]"  nsresult: "0x80040111 (NS_ERROR_NOT_AVAILABLE)"

How can I know before issuing frame.isNative that it will fail?

Thanks,
John.
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