CLIENT-2797: Allowing inner Exception to be null in AerospikeExceptio…

…n constructor

Several AerospikeException.Timeout constructors take an optional null inner exception and use this constructor.

Right now, using these AerospikeException.Timeout constructors will result in an "Object reference not set to an instance of an object" error if no inner exception is given.

AerospikeClient/Main/AerospikeException.cs

@@ -36,7 +36,7 @@ public AerospikeException(int resultCode, string message, Exception inner = null
 		}
 
 		public AerospikeException(int resultCode, Exception e)
-			: base(e.Message, e)
+			: base(e?.Message ?? string.Empty, e)
 		{
 			this.resultCode = resultCode;
 		}