@Nullable
  private Ref<PyExpression> resolveStringIndex(@NotNull PyExpression valueExpr, @NotNull String indexElement) {
    if (valueExpr instanceof PyCallExpression) {
      return resolveDictCall((PyCallExpression)valueExpr, indexElement, false);
    }
    else if (valueExpr instanceof PyDictLiteralExpression) {
      Ref<PyExpression> resolvedRef = getElementFromDictLiteral((PyDictLiteralExpression)valueExpr, indexElement);
      if (resolvedRef != null) return resolvedRef;
    }
    else if (valueExpr instanceof PyReferenceExpression) {
      return Ref.create(valueExpr);
    }

    return null;
  }
@Nullable
  private Ref<PyExpression> resolveStringIndex(@NotNull PyExpression valueExpr, @NotNull String indexElement)