mime: duplicate parameter name error

[iceking2nd]

I received an email. The Content-Type section contains two charset fields, but the contents of the two charset fields only differ in case. When parsing the email, the following error was reported.
letters.EmailParser.Parse: cannot parse part "multipart/mixed" with boundary "33cef21196996d27cfa60191f95633db16e292796ab85c9c48e957fb63e7": letters.parsers.parsePart: cannot parse Content-Type: letters.parsers.parseContentTypeHeader: cannot parse Content-Type "text/html; charset=utf-8; charset=UTF-8": letters.parsers.parseDefaultMediaType: cannot parse Content-Type "text/html; charset=utf-8; charset=UTF-8": mime: duplicate parameter name
Any ideas?

[mnako]

Thank you for opening the issue, @iceking2nd.

I believe that the best way to handle this and other similar edge cases will be offered in #134. Once the discussion and review there is finished, I will come back to this issue and add an example of how a custom parser can be used to solve this.