Oak, `ctx.assert`, and middleware

import { Application, Context } from "https://deno.land/x/oak@v12.4.0/mod.ts";

interface MyState {
  value: null | 3;
}

const app = new Application<MyState>({
  state: {
    value: 3,
  },
});

app
  .use((ctx: Context<MyState>) => {
    ctx.assert(ctx.state.value !== null, 500);
  })
  .use((ctx) => {
    // 'ctx.state.value' is possibly 'null'.deno-ts(18047)
    console.log(ctx.state.value + 5);
  });