Determine the {@link MimeType} of a message from the given MessageHeaders.
@param headers the headers to use for the resolution
@return the resolved {@code MimeType}, or {@code null} if none found
@throws InvalidMimeTypeException if the content type is a string that cannot be parsed
@throws IllegalArgumentException if there is a content type but its type is unknown
Determine the {@link MimeType} of a message from the given MessageHeaders. @param headers the headers to use for the resolution @return the resolved {@code MimeType}, or {@code null} if none found @throws InvalidMimeTypeException if the content type is a string that cannot be parsed @throws IllegalArgumentException if there is a content type but its type is unknown