Error While Retrieving URL form Document ID

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SharePoint2013

Whenever I am using the method to retrieve the document url from document id (Reference - Document ID Feature[^]), I am getting an error array out of bound, although the document id is present within the site collection. Actually it was working fine a week back. but suddenly this week the error seems to pop up every time. I again assure you that the document ID is still present. Can you tell me what can be the possible reason? (It's getting the instance of document id provider. But the var result field is null).