NEST version: 1.5.0
System.ArgumentException: An item with the same key has already been added.
at System.ThrowHelper.ThrowArgumentException (ExceptionResource resource) <0x4151e330 + 0x00039> in <filename unknown>:0
at System.Collections.Generic.Dictionary`2[TKey,TValue].Insert (System.Collections.Generic.TKey key, System.Collections.Generic.TValue value, Boolean add) <0x41101000 + 0x0019b> in <filename unknown>:0
at System.Collections.Generic.Dictionary`2[TKey,TValue].Add (System.Collections.Generic.TKey key, System.Collections.Generic.TValue value) <0x4114c880 + 0x00023> in <filename unknown>:0
at System.Collections.ObjectModel.KeyedCollection`2[TKey,TItem].AddKey (System.Collections.ObjectModel.TKey key, System.Collections.ObjectModel.TItem item) <0x414b62f0 + 0x00045> in <filename unknown>:0
at System.Collections.ObjectModel.KeyedCollection`2[TKey,TItem].InsertItem (Int32 index, System.Collections.ObjectModel.TItem item) <0x414b6240 + 0x0004b> in <filename unknown>:0
at System.Colle