Return default(K) when requesting a single value from Hits fields
Return default(K) when requesting a single value from Hits fields

If the hits fields contain no values, then null is returned for the typed array, causing a null reference exception when attempting to access the first value or default. Check for this and return default(K) when array is null

Cherry pick from 2.x af468f9648d076b0d700d98d7ebde5ca400b919d

elastic/elasticsearch-net,CSGOpenSource/elasticsearch-net,adam-mccoy/elasticsearch-net,elastic/elasticsearch-net,TheFireCookie/elasticsearch-net,CSGOpenSource/elasticsearch-net,adam-mccoy/elasticsearch-net,CSGOpenSource/elasticsearch-net,adam-mccoy/elasticsearch-net,TheFireCookie/elasticsearch-net,TheFireCookie/elasticsearch-net