Error from SharePoint site: Data is Null. This method or property cannot be called on Null values.

Though the above mentioned problem can be caused by so many other things but one of the probable cause in mentioned in the solution section.
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Problem:
I have 2 site collection within a web application.
http://server:9999/sites/1
http://server:9999/sites/2
Crawler is able to crawel Site Collection 1 whereas not site collection 2 and giving following error. Errorinfo is "Error from SharePoint site: Data is Null. This method or property cannot be called on Null values."
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Solution: (Groups means SiteGroup)
We have got solution to his problem (along with MS Premier Support Team).
THere was a probem with Description field value of Groups. While creating a Groups in SharePoint 2010 - using SP2010 Object model we were supplying NULL as description but SharePoint 2010 Search Crawler DO NOT LIKE IT. Groups must have some description attached to it.

But the amazing thing is while creating a group with NULL as description it will get created. So at first GROUPS should not have created.

Once we got the source of issue we created a small app to update the description of Group and Crawl was back to normal.