jfelchner/ruby-progressbar — pull request #78 by mmannerm (2014-06-27 07:18:32+00:00)
Title: Ensure output_string is not nil, which may happen for non-TTY output.

String[start,length] may return nil if the initial index falls outside the strength or the length is negative. Therefore the output_string may be nil for non-TTY cases, where for example stop() is called for unknown length files in middle of transaction, etc.