The CBT server reads the empty string on the right side of an open interval as the special value "infinity".

In particular, our current implementation of RowRange::Empty() is in fact turned into "all row keys except the empty string", because we send ("", "") and this is translated to ["\0", infinity) internally.

There is an easy fix to Empty(), using ("", "\0"):

result.row_range_.set_end_key_open(std::string("\0", 1));

but this reveals further bugs in the code, such as that RowRange::IsEmpty() does not recognize this as the empty range that it is.