Currently, the contentType.properties file list is not complete, for example, svg/svgz is not listed. Either we maintain it manually, or use other java class that hold all mime types, such as http://docs.oracle.com/javaee/7/api/javax/ws/rs/core/MediaType.html, http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/net/MediaType.html or https://tika.apache.org/.

Or consider a reasonable default content type for undetected content types, currently it returns ";charset=UTF-8;charset=UTF-8" in the response header (see attached sample) which make no sense.