在 Material-UI 中使用自定义主题时已弃用版式警告

在下面的代码中，我在 Material-UI 中使用了自定义主题：

import React from "react";
import ReactDOM from "react-dom";
import { MuiThemeProvider, createMuiTheme } from "@material-ui/core/styles";
import Button from "@material-ui/core/Button";
import { purple, green } from "@material-ui/core/colors";

const theme = createMuiTheme({
  palette: {
    primary: purple,
    secondary: green
  }
});

function App() {
  return (
    <MuiThemeProvider theme={theme}>
      <Button color="primary">Button1</Button>
      <Button color="secondary">Button2</Button>
    </MuiThemeProvider>
  );
}

ReactDOM.render(<App />, document.getElementById("root"));

我收到以下警告： Warning: Material-UI: you are using the deprecated typography variants that will be removed in the next major release.

我没有使用任何排版（更不用说任何已弃用的排版变体）

为什么我会收到此警告？有人可以解释一下吗？
完整演示请参见codesandbox：https://codesandbox.io/s/r5v9pjxnq4 https://codesandbox.io/s/r5v9pjxnq4

最小重现代码：https://codesandbox.io/s/p9628o7wlj https://codesandbox.io/s/p9628o7wlj
（结果只是使用createMuiTheme还给出警告！）

我只是添加我的index.html:

<script>window.__MUI_USE_NEXT_TYPOGRAPHY_VARIANTS__ = true</script>