static @Nullable("null means enabled, notnull means disabled and contains error message") FailReason checkCanConvert(@NotNull VirtualFile virtualFile) {
    if (virtualFile.isDirectory()) {
      return FailReason.IS_DIRECTORY;
    }

    Charset charsetFromContent = EncodingManagerImpl.computeCharsetFromContent(virtualFile);
    return charsetFromContent != null ? FailReason.BY_FILE : fileTypeDescriptionError(virtualFile);
  }
static @Nullable("null means enabled, notnull means disabled and contains error message") FailReason checkCanConvert(@NotNull VirtualFile virtualFile)