code: private void checkContentType(String contentType) {
  		if(contentType == null) {
  			throw new IllegalArgumentException("the content type cannot be null");
  		}
  		int indexOfSlash = contentType.indexOf("/");
  		if(indexOfSlash != -1) {
  			if(!JainSipUtils.IANA_ALLOWED_CONTENT_TYPES.contains(contentType.substring(0, indexOfSlash))) {
  				throw new IllegalArgumentException("the given content type " + contentType + " is not allowed");
  			}
  		} else if(!JainSipUtils.IANA_ALLOWED_CONTENT_TYPES.contains(contentType.toLowerCase())) {
  			throw new IllegalArgumentException("the given content type " + contentType + " is not allowed");
  		}
  	}
docs: Check the content type against the list defined by the iana
  http://www.iana.org/assignments/media-types/
  @param contentType