function assertExistsimport { assertExists } from "https://dotland.deno.dev/std@0.145.0/testing/asserts.ts"; assertExists<T>(actual: T, msg?: string): asserts actual is NonNullable<T>Make an assertion that actual is not null or undefined. If not then throw. Make an assertion that actual is not null or undefined. If not then throw. Type ParametersTParametersactual: Toptionalmsg: stringReturnsasserts actual is NonNullable<T>