Deno adds "| undefined" to everything

When trying to call a value from an object or Record directly by its key, deno says object might be undefined for some reason.

const objectList: Record<string, number[]> = {
  'itemOne': [1, 2, 3],
  'itemTwo': [4, 5, 6]
}

const numberArray: number[] = objectList['itemOne']

const objectList: Record<string, number[]> = {
  'itemOne': [1, 2, 3],
  'itemTwo': [4, 5, 6]
}

const numberArray: number[] = objectList['itemOne']

const objectList: Record<string, number[]> = {
  'itemOne': [1, 2, 3],
  'itemTwo': [4, 5, 6]
}

const numberArray: number[] = objectList['itemOne']

const objectList: Record<string, number[]> = {
  'itemOne': [1, 2, 3],
  'itemTwo': [4, 5, 6]
}

const numberArray: number[] = objectList['itemOne']

gives me

Type 'number[] | undefined' is not assignable to type 'number[]'.
  Type 'undefined' is not assignable to type 'number[]'.deno-ts(2322)

Type 'number[] | undefined' is not assignable to type 'number[]'.
  Type 'undefined' is not assignable to type 'number[]'.deno-ts(2322)

Type 'number[] | undefined' is not assignable to type 'number[]'.
  Type 'undefined' is not assignable to type 'number[]'.deno-ts(2322)

Type 'number[] | undefined' is not assignable to type 'number[]'.
  Type 'undefined' is not assignable to type 'number[]'.deno-ts(2322)

why.