public static @Nullable String getMimeTypeFromExtension(String extension) {
    String result = sExtensionToMimeTypeMap.get(extension);
    if (result != null) {
      return result;
    }
    return sMimeTypeMap.getMimeTypeFromExtension(extension);
  }
Wrapper around the system's {@link MimeTypeMap} that also handles types it doesn't support.
fbcore/src/main/java/com/facebook/common/media/MimeTypeMapWrapper.java