@Contract("_, !null -> !null")
  public PsiSubstitutor findNestedSubstitutor(PsiElement arg, @Nullable PsiSubstitutor defaultSession) {
    InferenceSession session = myNestedSessions.get(PsiTreeUtil.getParentOfType(arg, PsiCall.class));
    return session == null ? defaultSession : session.getInferenceSubstitution();
  }
@Contract("_, !null -> !null")
  public PsiSubstitutor findNestedSubstitutor(PsiElement arg, @Nullable PsiSubstitutor defaultSession)