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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_content_type(self):
 """Return the message's content type. The returned string is coerced to lower case of the form `maintype/subtype'. If there was no Content-Type header in the message, the default type as given by get_default_type() will be returned. Since according to RFC 2045, messages always have a default type this will always return a value. RFC 2045 defines a message's default type to be text/plain unless it appears inside a multipart/digest container, in which case it would be message/rfc822. """

        missing = object()
        value = self.get('content-type', missing)
        if value is missing:
            # This should have no parameters
            return self.get_default_type()
        ctype = _splitparam(value)[0].lower()
        # RFC 2045, section 5.2 says if its invalid, use text/plain
        if ctype.count('/') != 1:
            return 'text/plain'
        return ctype