Orphans sites causing search to fail

Search results not returned and instead throw a correlation id error with below error found in ULS   ############  0x5304  SharePoint Server Search     Query    afpkb     Unexpected        Getting results failed: System.NullReferenceException: Object reference not set to an instance of an object.     at Microsoft.Office.Server.Search.Administration.UrlMapper.ExtractMapping(Pair`2 properties, SPSite site, IDictionary`2 urlMapping, IDictionary`2 reverseUrlMapping)     at Microsoft.Office.Server.Search.Administration.UrlMapper.GetNewCacheEntry(Pair`2 properties)     at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key,…

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