message: refactor(labware-creator): refactor onUpload for TS correctness
  Closes
diff: @@ -384,15 +384,10 @@ export const LabwareCreator = (): JSX.Element => {
  | React.DragEvent<HTMLLabelElement>
  | React.ChangeEvent<HTMLInputElement>
  ) => {
  - // TODO(IL, 2021-03-31): should be new Filelist() or maybe null, FileList isn't an array []. Can drop the never[] type!
  let files: FileList | never[] = []
  - // @ts-expect-error(IL, 2021-03-31): need to do `'event' in dataTransfer`
  - if (event.dataTransfer && event.dataTransfer.files) {
  - // @ts-expect-error(IL, 2021-03-31): same
  + if ('dataTransfer' in event && event.dataTransfer.files !== null) {
  files = event.dataTransfer.files
  - // @ts-expect-error(IL, 2021-03-31): need to do `'files' in event.target`
  - } else if (event.target.files) {
  - // @ts-expect-error(IL, 2021-03-31): same
  + } else if ('files' in event.target && event.target.files !== null) {
  files = event.target.files
  }
  @@ -400,8 +395,9 @@ export const LabwareCreator = (): JSX.Element => {
  const reader = new FileReader()
  // reset the state of the input to allow file re-uploads
  - // @ts-expect-error(IL, 2021-03-31): need to do conditional to disabiguate the union
  + if ('value' in event.currentTarget) {
  event.currentTarget.value = ''
  + }
  if (!file.name.endsWith('.json')) {
  setImportError({ key: 'INVALID_FILE_TYPE' })
  