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
Resolve the content type for a message.
@author Rossen Stoyanchev @since 4.0