That seems like a breaking change in a patch release of diff-lcs then.  Does this mean that users who upgrade diff-lcs (or get 1.2.2 pulled in by bundler) will start to get errors from rspec-expectations 2.13's use of diff-lcs?  That seems like a big problem.

Also, if we don't have a first chunk of data, but there is a 2nd chunk of data, shouldn't diff-lcs use the encoding of the second chunk?  Seems like the encoding it will use based on this string we are adding will not necessarily match the encoding of the second chunk...