fails:Struct#dig returns the nested value specified by the sequence of keys
fails:Struct#dig returns the nested value specified if the sequence includes an index
fails:Struct#dig returns nil if any intermediate step is nil
fails:Struct#dig raises a TypeError if any intermediate step does not respond to #dig
fails:Struct#dig raises an ArgumentError if no arguments provided
fails:Struct#dig calls #dig on any intermediate step with the rest of the sequence as arguments
