Ruby

merge revision(s) 61639: [Backport #14323]

    net/ftp: fix FrozenError in BufferedSocket

    I noticed this bug while working on something else with
    RUBYOPT=-d on, existing test cases all passed with it.

    Note: I use String.new because it is the local style, here,
    I prefer +'' (or ''.b, for a future commit)

    * lib/net/ftp.rb (BufferedSocket#read): use String.new
    * test/net/ftp/test_buffered_socket.rb (test_read_nil): new test
      [ruby-core:84675] [Bug #14323]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@62867 b2dd03c8-39d4-4d8f-98ff-823fe69b080e