public @NotNull <S extends StubElement<?>, Psi extends PsiElement> Psi getRequiredStubOrPsiChild(@NotNull IStubElementType<S, Psi> elementType) {
    Psi result = getStubOrPsiChild(elementType);
    if (result == null) {
      throw new AssertionError("Missing required child of type " + elementType + "; tree: " + DebugUtil.psiToString(this, true));
    }
    return result;
  }
public @NotNull <S extends StubElement<?>, Psi extends PsiElement> Psi getRequiredStubOrPsiChild(@NotNull IStubElementType<S, Psi> elementType)