private @Nullable PsiFile getContainingFileForClass(@NotNull String fqn) {
    String filename = fqn;
    if (fqn.contains(".")) {
      filename = fqn.substring(fqn.lastIndexOf('.') + 1);
    }
    if (filename.contains("$")) {
      filename = filename.substring(0, filename.indexOf('$'));
    }
    filename += ".java";
    PsiFile[] files = FilenameIndex.getFilesByName(myProject, filename, GlobalSearchScope.allScope(myProject));
    return ArrayUtil.getFirstElement(files);
  }
private @Nullable PsiFile getContainingFileForClass(@NotNull String fqn)