Incompatible character encodings with ruby 2.1.2  #9

Sorry to bother again but after some testing I noticed another issue.

I have my email file in variable 'msg'. Performing the following command shows the expected output (same as Ruby 1.8.7)
msg.to_mime
=> #< Mime content_type="multipart/alternative" >

However, when I call to_s, I receive an error with Ruby 2.1.2
msg.to_mime.to_s
Encoding::CompatibilityError: incompatible character encodings: UTF-8 and ASCII-8BIT
from /Users/user/.rbenv/versions/2.1.2/gemsets/workers/gems/ruby-msg 1.5.2/lib/mapi/mime.rb:109:in join' from /Users/user/.rbenv/versions/2.1.2/gemsets/workers/gems/ruby-msg 1.5.2/lib/mapi/mime.rb:109:into_s'

When researching the issue, I replaced the following in lib/mapi/mime.rb#108:
part.to_s(opts)
with
part.to_s(opts).encode("UTF-8", :invalid=>:replace, :undef => :replace, :replace => "")

After I made that change to add the .encode in mime.rb, I was able to get my emails to convert correctly.

I also see that the 'parts' of my email are different encodings which I believe is what the error is referring to.
irb(main):003:0> msg.to_mime.parts.each do |part|
irb(main):004:1* puts part.to_s.encoding
irb(main):005:1> end; nil
UTF-8
ASCII-8BIT

Thus, by removing the above change to mime.rb and adding the .encode method in lib/mapi/convert/note_mime.rb#159 on the "props.body_html" also allows the email to convert correctly (that is the 'part' that is being encoded as ASCII-8BIT).

Not sure of the exact way to fix this permanently. If there is any other information I can provide I will be glad to do so.

Thanks for your help!